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THE 


CHEMISTRY  OF  AGRICULTURE 


FOR  STUDENTS  AND  FARMERS 


BY 


CHARLES  W.  STODDART,  Ph.D. 

DEAN,  SCHOOL  OF  THE  LIBERAL  ARTS,  PENNSYLVANIA  STATE  COLLEGE 

SECOND  EDITION,  THOROUGHLY  REVISED 
ILLUSTRATED  WITH   83   ENGRAVINGS  AND   1    PLATE 


LEA   &   FEBIGER 

PHILADELPHIA  AND   NEW   YORK 
1921 


Copyright 

LEA  &  FEBIGER 

1921 


.«».     •••   .'. 


t  •  •  \    .'- 


t8l> 


PREFACE  TO  THE  SECOND  EDITION 


In  preparing  the  second  edition  some  changes  have  been 
made,  notably-  the  omission  of  the  summary  at  the  end  of 
each  chapter  and  the  addition  of  a  Hst  of  suggestive  exercises 
designed  to  make  the  student  think.  The  subject-matter 
presented  in  the  text  can,  in  this  way,  be  brought  more 
forcefully  to  the  attention  of  the  reader  and  the  facts  applied 
to  practical  conditions.  There  have  also  been  added  sections 
on  new  fertilizer  materials,  showing  the  development  of 
our  own  potash  resources  as  a  result  of  the  Great  War,  and 
also  of  synthetic  nitrogenous  fertilizers. 

More  material  has  been  inserted  where  it  seemed  desirable; 
parts  have  been  rewritten  to  make  the  subject  clearer;  and 
an  attempt  has  been  made  to  eliminate  errors  that  crept  into 
the  first  edition.  The  order  of  the  first  three  chapters  has 
been  changed  to  facilitate  the  teaching  of  the  subject- 
matter. 

The  questions  at  the  end  of  the  chapters,  many  criticisms, 

and  some  of  the  additional  material  have  been  the  work  of 

Professor  M.  W.  Lisse.    To  him  the  author  wishes  to  express 

his  gratitude  and  esteem. 

C.  W.  S. 
State  College,  Pa. 


(V) 


480546 


PREFACE  TO  THE  FIRST  EDITION 


There  is  at  present  need  for  a  text  on  general  agricultural 
chemistry  which  will  cover  the  field  briefly,  in  a  logical 
manner,  giving  only  the  facts,  and  not  consisting  of  a  dis- 
connected series  of  quotations  and  tables  from  the  very 
extended  literature  of  the  subject.  The  need  for  such  a 
text  has  been  particularly  marked  in  teaching  large  classes 
of  students  at  The  Pennsylvania  State  College.  As  a  con- 
sequence the  present  book  has  been  written.  While  it  is 
intended  primarily  for  students  who  have  had  previous 
training  in  Botany,  Chemistry,  Geology  and  Physics,  it  is 
suflBciently  elementary  to  make  it  of  value  to  any  intelligent 
person. 

Concerning  some  of  the  statements  made  in  the  text  it 
is  well  known  that  a  difference  of  opinion  exists  among 
authorities,  but  it  is  deemed  better  to  present  them  as  facts 
rather  than  to  give  the  various  arguments  or  to  omit  them 
altogether. 

Since  the  raising  of  crop  plants  is  the  fundamental  business 
of  agriculture,  and  since  on  them  depend  the  life  and  growth 
of  animals,  there  is  discussed  first  the  plant,  its  germination, 
-growth,  and  products.  Then  are  taken  up  the  various 
conditions  necessary  for  plant  growth,  such  as  the  atmos- 
phere, soil,  fertilizers,  and  spray  materials.  A  short  chapter 
on  the  gas  engine  is  inserted  at  this  point,  since  the  increasing 
use  of  power  on  the  farm  in  the  raising  and  marketing  of 

(vii) 


VlU  PREFACE  TO   THE  FIRST  EDITION 

crops  makes  some  knowledge  of  the  chemistry  of  gasoline 
and  carburetion  important.  Finally  the  animal  is  considered, 
together  with  its  food,  digestion,  and  products. 

The  references  at  the  end  of  each  chapter  give  the  principal 
sources  of  information  used  in  the  preparation  of  this  text. 
While  the  lists  are  by  no  means  complete,  they  will  be  of 
help  for  any  who  desire  to  pursue  the  subject  further. 

The  thanks  of  the  author  are  due  to  the  German  Kali 
Works,  "La  Hacienda,"  Great  Western  Sugar  Co.,  Economy 
Silo  and  Manufacturing  Co.,  Chilean  Nitrate  Propaganda, 
American  Coal  Products  Co.,  C.  Tennarit  Sons  &  Co., 
American  Cyanamid  Co.,  and  the  Avery  Co.,  for  many 
of  the  illustrations.  Particularly  is  the  author  indebted 
to  Dr.  M.  B.  MacDonald,  Mr.  F.  P.  Weaver,  and  Mr. 
R.  U.  Blasingame  for  helpful  suggestions,  and  to  Messrs. 
C.  A.  Smith  and  E.  DeTurk  for  some  of  the  drawings^ 

C.  W.  S. 

State  College,  Pa. 


CONTENTS 

PART  I 
THE  PLANT 


CHAPTER  I 
Plant  Compounds 17 

CHAPTER  II 
Germination  of  the  Seed 72 

CHAPTER  III 
Gkowth  of  the  Plant 80 

CHAPTER  IV 
Crops 102 


PART  II 
FACTORS  IN  PLANT  GROWTH 


CHAPTER  V 
The  Air 125 

CHAPTER  VI 
The  Soil:  Organic  Matter 132 

CHAPTER  VII 
The  Soil:  Inorganic  Matter 153 

CHAPTER  VIII 

Fertilizers 186 

(ix) 


X  CONTENTS 

CHAPTER  IX 
Nitrogenous  Fertilizers 192 

CHAPTER  X 
Phosphate  Fertilizers 206 

CHAPTER  XI 
Potash  Fertilizers 216 

CHAPTER  XII 
Lime 224 

CHAPTER  XIII 
Farm  Manure        241 

CHAPTER  XIV 
Soil  and  Fertilizer  Analysis 256 

CHAPTER  XV 
Insecticides  and  Fungicides 264 

CHAPTER  XVI 
The  Gas  Engine 279 


PART  III 
THE  ANIMAL 


CHAPTER  XVII 
The  Chemistry  of  Animal  Physiology 287 

CHAPTER  XVIII 
Food  and  Digestion 304 

CHAPTER  XIX 

Milk  and  Dairy  Products        318 


THE  CHEMISTRY  OF  AGRICULTURE 


PART  I 

THE  PLANT 


CHAPTER  I 
PLANT  COMPOUNDS 

There  are  a  very  large  number  of  organic  compounds 
produced  during  the  growth  of  plants.  Some  plants  form 
one  kind,  some  another.  Many  of  the  compounds  have  no 
value  commercially,  and  no  known  value  physiologically. 
Some  are  evidently  merely  by-products,  whereas  others 
undoubtedly  serve  some  useful  purpose  to  the  plant.  Since 
many  of  these  compounds  are  of  great  importance  to  the 
human  race,  it  is  necessary  to  know  something  of  their  proper- 
ties and  uses  outside  of  the  plant.  In  the  following  discussion 
only  those  plant  compounds  which  are  of  known  physiological 
importance  to  the  plant,  and  particularly  those  which  are  of 
economic  importance  to  mankind,  will  be  considered.  For 
convenience  the  various  compounds  will  be  grouped  as 
follows: 

L     Carbohydrates 
IL     Fixed  Oils  and  Waxes 

IIL    Volatile  Oils  and  Resins 

IV.     Nitrogenous  Compounds 
V.    Organic  Acids  and  their  Salts 
2  (17) 


18  PLANT  COMPOUNDS 


I.    CARBOHYDRATES 


1.  General  Definition. — ^The  most  abundant  group  of 
organic  compounds  is  that  of  the  carbohydrates  or  sac- 
charides, comprising  about  75  per  cent,  of  the  dry  matter 
of  plants.  Popularly,  a  carbohydrate  is  defined  as  a  com- 
pound containing  carbon,  hydrogen,  and  oxygen,  with  the 
hydrogen  and  oxygen  in  the  same  proportion  as  in  water; 
or,  a  compound  of  carbon  and  water,  thus:  Dextrose  = 
6C+6H2O.  This  definition,  while  not  exactly  correct,  will 
hold  in  a  majority  of  cases  and  serves  very  well  to  dis- 
tinguish the  group.  The  exceptions  to  this  statement  are 
principally  acetic  acid,  whose  empirical  formula  is  C2H4O2, 
but  whose  graphic  formula  is  CH3COOH,  showing  the  acid 
or  carboxvl  group;  and  lactic  acid,  CsHeOs,  but  otherwise 
written  CH3.CHOH.COOH. 

A  carbohydrate  may  be  defined  more  accurately  as  a 
compound  containing  always  one  or  more  hydroxyl  (OH) 
groups,  and  usually  either  an  aldehyde 

H  O 

II  ,    ,  I      II      I 

(— c— c=0)  or  ketone  (_c— c— c— )  group. 

I  II- 

The  presence  of  the  aldehyde  group  indicates  that  the 
carbohydrate  is  easily  oxidized,  whereas  the  presence  of  the 
ketone  group  usually,  though  not  always,  indicates  that  the 
carbohydrate  is  not  easily  oxidized.  The  principal  carbo- 
hydrates contain  carbon  atoms  to  the  number  of  six  or  a 
multiple  of  six.  The  carbohydrates  are  divided  into  two 
general  classes,  the  Sugars  including  the  monosaccharides 
and  disaccharides;  and  the  Non-Sugars  or  Polysaccharides. 

2.  Sugars. — ^As  a  class  the  sugars  are  colorless,  odor- 
less, crystalline  compounds,  soluble  in  water,  and,  ordinarily, 
sweet  in  taste.  Their  most  characteristic  property  is  that 
of  optical  activity,  that  is,  they  rotate  the  plane  of  polarized 


CARBOHYDRATES  19 

light  either  to  the  right  or  to  the  left.^  The  simple  sugars, 
or  monosaccharides,  contain  from  two  to  nine  carbon  atoms, 
and  are  named  according  to  the  number  of  carbon  atoms  in 
the  molecule:  Dioses,  trioses,  tetroses,  etc.  Each  molecule 
consists  of  a  single  "sugar"  group  of  atoms.  The  only 
important  monosaccharides  are  the  hexoses,  or  sugars  con- 
taining six  carbon  atoms,  C6H12O6.  Dextrose  and  levulose 
are  the  best  examples  of  hexoses.  The  disaccharides  are 
formed  by  the  condensation  of  two  molecules  of  a  monosac- 
charide with  the  elimination  of  one  molecule  of  water.  Each 
molecule  of  a  disaccharide,  then,  consists  of  two  single 
"sugar"  groups  of  atoms.  Sucrose  and  maltose  are  the 
principle  disaccharides  found  in  plants. 

*  Optical  Activity :  An  ordinary  ray  of  light  is  supposed  to  consist  of 
particles  vibrating  in  every  direction  at  right  angles  to  the  direction  of  the 
ray.  When  such  a  ray  is  passed  through  a  properly  cut  crystal  of  Iceland 
spar  called  a  Nicol  prism,  it  is  separated  into  two  rays,  one  of  which  is 
reflected  out  to  one  side  of  the  prism,  and  the  other  passes  through,  its 
particles  now  vibrating  in  only  one  plane.  This  ray  is  said  to  be  polarized, 
and  substances  which  have  the  power  of  rotating  this  plane  of  polarized 
light  in  one  direction  or  the  other  are  said  to  be  optically  active,  either 
dextrorotatory  ( +)  or  levorotatory  (  —  )  as  they  turn  the  plane  of  polarized 
light  to  the  right  or  to  the  left.  The  amount  of  rotation  depends  on  the 
specific  property  of  the  substance  and  the  number  of  molecules  through 
which  the  light  passes.  The  amount  of  rotation  can  be  measured,  and  by 
calculation  the  percentage  composition  of  sugar  or  other  substance  can  be 
determined  in  a  solution.  The  instrument  for  measuring  the  amount  of 
rotation  is  called  a  polariscope,  or,  since  it  is  used  mostly  for  the  determina- 
tion of  sugar,  a  saccharimeter.  It  consists  essentially  of  a  tube  containing 
at  one  end  a  polarizing  prism  which  polarizes  a  ray  of  light  from  some  source, 
and  an  analyzing  prism  at  the  other  end  mounted  on  a  revolving  disk  gradu- 
ated into  degrees.  Between  the  two  prisms  is  a  trough  in  which  may  be 
placed  a  tube,  closed  at  both  ends  with  glass,  containing  the  solution  to  be 
examined.  The  polarized  light  if  undisturbed  passes  through  the  analyzer 
and  illuminates  the  field  of  vision  through  an  eye-piece.  If  the  ray  is  rotated 
by  an  optically  active  substance,  the  light  does  not  pass  through  the  analyzer 
and  the  field  of  vision  is  darkened.  If  the  analyzer  is  now  rotated  to  the  right 
or  left,  as  the  case  may  be,  just  as  much  as  the  substance  rotates  the  polarized 
ray,  the  field  of  vision,  will  again  be  brightly  illuminated.  There  are  many 
modifications  of  this  polariscope  tending  to  increase  the  accuracy  of  obser- 
vation, but  the  principle  is  the  same  in  all  of  the  instruments.  For  com- 
paring the  rotatory  power  of  different  substances,  there  is  used  the  term 
specific  rotation  which  is  the  amount  of  dextro-  or  levorotation  of  plane 
polarized  sodium  light  caused  by  a  solution  10  cm.  long,  each  cubic  centi- 
meter of  which  contains  one  gram  of  substance,  at  a  temperature  of  20°  C. 


20 


PLANT  COMPOUNDS 


3.    Dextrose,  Glucose,  Grape  Sugar. — C6H12O6,  graphically: 

H 

I 

H— C— O— H 

I 
H— C— O— H 

I 
H— C— O— H 

H— C— O— H 

I 
H— C— O— H 

H— C=0 

This  constitutes  what  may  be  termed  a  single  "sugar" 
group  of  atoms,  hence,  monosaccharide.  It  is  found  free  in 
nature  in  all  parts  of  the  plant,  but  for  the  most  part  it  occurs 
associated  with  an  equal  quantity  of  levulose  in  such  sweet 
fruits  as  grapes,  cherries,  and  pears.  It  is  also  found  in 
onions.  Dextrose  occurs  in  glucosides^  in  combination  with 
different  kinds  of  compounds  such  as  alcohols,  acids,  and 
aldehydes,  which  hydrolyze  naturally  under  the  action  of 
enzymes  to  form  glucose  and  the  other  compounds.  It  is 
formed  in  nature  (Section  62)  by  the  condensation  of  for- 
maldehyde in  the  leaf,  and  by  hydrolytic  enzyme  (Section 
46)  action  on  such  storage  forms  of  carbohydrates  as  starch 
and  sucrose  (Section  63). 


1  The  formation  of  a  glucoside  can  best  be  seen  from  a  graphic  formula: 

H  H 

I 
H— C— O— H 

I 
H— C— O— H 

I 
— O— R    =  H— C— 0 1  +  H2O 

I 
H— C— O— H 

I  I 

H— C— O— H   I 

H— C^^^ O— R 


R  represents  the  alkyl  group  of  an  alcohol,  acid,  aldehyde,  or  ketone. 


CARBOHYDRATES  21 

Physiologically  dextrose  is  the  usual  transport  form  of 
carbohydrates,  but  occasionally  it  is  the  storage  form,  as  in 
the  onion.  Dextrose  is  a  nearly  white  solid,  easily  soluble 
in  water  and  in  hot  alcohol,  insoluble  in  ether,  crystallizes 
as  a  hydrate,  C6H12O6.H2O,  from  water,  and  in  the  dehydrated 
form  from  alcohol  (Fig.  1).  It  is  not  as  sweet  as  ordinary 
sugar.    It  is  dextrorotatory,  from  which  fact  it  gets  the  name 


Fig.  1. — Crystals  of  anhydrous  dextrose.     Magnified.     Drawing  Uy 
C.  A.  Smith. 


dextrose,  "right  sugar."  The  specif c  rotation  of  ordinary 
dextrose  is  +52.5°.  Since  it  contains  the  aldehyde  group 
it  is  easily  oxidized  to  various  compounds.  This  oxidation  is 
measured  by  the  equivalent  reduction  of  what  is  called 
Fehling's  solution^  and  this  reduction  of  Fehling's  solution 
is   a   characteristic  reaction   for   dextrose.     Dextrose   also 

•  Fehling's  solution  is  made  by  mixing  equal  parts  of  a  solution  of  copper 
sulphate  with  a  solution  of  sodium  potassium  tartrate  (Rochelle  salts) 
in  sodium  hydroxide.  The  sodium  hydroxide  forms  copper  hydroxide  which 
dissolves  to  a  deep  blue  color  in  the  sodium  potassium  tartrate.  The  copper 
hydroxide  in  solution  is  the  reacting  compound.  It  is  reduced  according 
to  the  following  equation  : 

4  Cu(0H)2  =  4  CuOH  +  2  HjO  +  O2. 

On  boiling  the  solution  the  yellow  cuprous  hydroxide,  4  CuOH,  changes 
to  the  brick  red  cuprous  oxide  and  water,  CusO+HjO.  The  amount  of 
red  precipitate  is  a  measure  of  the  amount  of  dextrose  in  solution. 


22  PLANT  COMPOUNDS 

unites  with  calcium  hydroxide  and  barium  hydroxide  to 
form  compounds  which  might  be  called  "dextrates"  or 
"dextroxides,"  CeHuOe.CaOH  and  CeHiiOe.BaOH.^  They 
are  soluble  in  water  but  insoluble  in  alcohol.  Dextrose 
is  easily  changed,  or  fermented,  by  fungi  and  bacteria  to 
alcohol  and  carbon  dioxide,  as  follows:  C6H12O6  =  2C2H5OH 
+  2CO2;  to  lactic  acid,  as  follows:  CeHiaOe  =  2CH3.CHOH.- 
COOH;  and  to  butvric  acid,  carbon  dioxide,  and  hydrogen, 
as  follows:  CeHisOe  =  CH3.CH2.CH2.COOH  +  2CO2  +  2H2. 
Pure  dextrose  can  be  made  by  the  hydrolysis  of  starch  or 
sucrose  with  dilute  hydrochloric  acid,  and  recrystallization 
from  hot  alcohol.  Commercial  glucose  is  made  in  this  country 
by  boiling  cornstarch  under  pressure  with  hydrochloric  acid, 
neutralizing  the  acid  with  sodium  carbonate,  and  clarifying 
the  liquid  with  bone  charcoal.  The  product  is  sold  as  a  thick, 
amber-colored  liquid  containing  30  to  40  per  cent,  of  dextrose, 
the  rest  being  dextrins  and  other  impurities.  By  boiling  the 
mass  longer  more  dextrins  are  converted  to  dextrose  and  a 
crystallizable  product  containing  70  to  80  per  cent,  dextrose 
is  obtained.  Glucose  is  used  largely  in  making  candy, 
jellies,  preserves,  table  syrup,  etc. 

1  Their  formation  can  be  best  illustrated  graphically.  The  exact  location 
of  the  hydroxyl  group  which  combines  with  the  base  is  not  known,  but  the 
one  chosen  will  at  least  illustrate  the  reaction: 


H.O 


H 

H 

1 

H— C— 0— H 

1 

H— C— 0— H 

H— C— 0— H 

1 

H— C— 0— H 

+ 

H— C— 0— H 

1 

H— C— 0— H 

1 

H— C— 0— H 

1 

Y 

H— C— 0— H 

1 
H— C— 0— Ca— 0- 

H— C=0 

H— C— 0- 

1 

-H  +  H 

— 0 

1 

-H 

H— C=0 

H— C 

CARBOHYDRATES  23 

4.    Levulose,  Fructose,  Fruit  Sugar. — C6Hi20«,  graphically: 

H 

I 

H— C— O— H 

I 
H— C— O— H 

I 
H— C— O— H 

I 

H— c— a— H 

I   . 

C-0 

I 

H— C— O— H 

I 

u 

This  constitutes  another  single  "sugar"  group  of  atoms. 
Levulose  is  found  in  plants,  particularly  the  sweet  fruits, 
and  nearly  always  with  dextrose.  Honey  is  almost  wholly 
a  mixture  of  levulose  and  dextrose.  Levulose  is  formed 
naturally  by  the  enzyme  hydrolysis  of  sucrose,  or  arti- 
ficially by  hydrolysis  of  sucrose  with  dilute  hydrochloric 
acid.  In  either  case  there  are  produced  equal  quantities 
of  dextrose  and  levulose.  Physiologically  it  probably  plays 
the  same  role  as  dextrose.  Levulose  is  a  white  solid,  crystal- 
lizable  with  considerable  difficulty,  very  soluble  in  water 
and  in  hot  alcohol.  It  is  much  more  strongly  levorotatory 
than  dextrose  is  dextrorotatory,  the  specific  rotation  being 
— 92.5°.  Hence  it  is  called  levulose,  "left  sugar."  It  is 
sweeter  than  dextrose.  Although  it  does  not  contain  an 
aldehyde  group  it  is  easily  oxidized,  that  is,  it  reduces 
Fehling's  solution.  Levulose  forms  compounds  with  calcium 
hydroxide  and  barium  hydroxide — "levulates" — insoluble  in 
water  and  in  alcohol.  It  is  fermented  by  fungi  and  bacteria 
like  dextrose.  One  way  to  make  it  is  to  boil  sucrose  with 
hydrochloric  acid  and  thereby  change  the  sucrose  to  dextrose 
and  levulose.  On  treating  the  cold  solution  with  an  excess 
of  calcium  hydroxide,  the  crystals  of  calcium  levulate 
are  precipitated  and  can  be  filtered.  On  decomposing  the 
precipitate  with  oxalic  acid,  and  concentrating  the  filtered 
solution,  levulose  will  crystallize  out.     Aside  from  its  use 


24 


PLANT  COMPOUNDS 


as  a  food  in  fruit  and  honey,  where  it  occurs  naturally, 
levulose  has  no  economic  importance. 

5.     Sucrose,   Saccharose,  Cane   Sugar. — C12H22O11,  graphi- 
cally : 


o— H 


This  constitutes  a  double  "sugar"  group  of  atoms  or  the 
union  of  two  single  groups.  Hence  it  is  a  disaccharide.  It 
is  very  widely  distributed  in  plants,  being  found  particularly 
in  sweet  fruits,  stalks  of  corn  and  sugar  cane,  in  seeds,  roots, 
bulbs,  and  the  sap  of  maple,  birch,  and  other  trees.  Sugar 
cane  and  sugar  beets  are  the  principal  sources  of  sucrose, 
the  former  containing  about  20  per  cent.,  the  latter,  15 
per  cent.  Fig.  2  illustrates  the  harvesting  of  a  crop  of 
sugar  cane,  and  Fig.  2  a  growing  crop  of  sugar  beets. 
From  the  physiological  point  of  view,  sucrose  is  a  storage 
form  of  carbohydrates,  particularly  in  roots  and  tubers  such 
as  beets  and  sweet  potatoes,  it  being  formed  in  all  proba- 
bility by  a  condensation  of  dextrose  and  the  elimination  of 
water. 

Sucrose  is  a  colorless  solid,  crystallizing  in  large,  clear  crys- 
tals (Fig.  3).  As  it  is  usually  purchased,  it  consists  of  very 
small  crystals,  the  mass  of  which  appears  white  because 
of  reflected  light.  It  is  easily  soluble  in  water,  slightly 
soluble  in  hot  absolute  alcohol,  more  easily  soluble  in  dilute 
alcohol,  insoluble  in  ether  and  in  cold  absolute  alcohol.  It 
is  dextrorotatory,  the  specific  rotation  being  +66.5°.  Its 
sweetness  is  too  well  known  to  need  description. 


CARBOHYDRATES 


25 


w 


26 


PLANT  COMPOUNDS 


Sucrose  does  not  reduce  Fehling's  solution,  that  is,  it  is 
not  easily  oxidized.  It  melts  at  about  160°  C.  From  170° 
up  to  190°  C.  it  decomposes,  by  losing  water,  to  a  mixture 
of  unknown  condensation  products,  the  mass  turning  brown 
in  color  and  having  a  peculiar,  agreeable  flavor.  Caramel 
is  the  name  given  to  the  material.  Caramel  is  soluble  in 
water,  reduces  Fehling's  solution,  and  is  used  to  a  large 
extent  as  flavoring  for  candy  and  ice-cream. 


Fig.  3. — Crystal  of  sucrose.    Natural  size.    Drawing  by  C.  A.  Smitli. 

Under  the  action  of  an  enzyme  (Section  46)  called  inver- 
tase,  sucrose  hydrolyzes  to  equal  parts  of  dextrose  and  levu- 
lose.^    This  is  the  way  it  changes  naturally  in  plants.    Arti- 

'  The  hydrolytic  change  of  sucrose  into  equal  parts  of  levulose  and  dex- 
trose is  shown  best  by  the  graphic  formula,  and  illustrates  very  well  the 
glucoside-like  character  of  the  sucrose  molecule.    (See  footnote  on  page  20.) 
In  fact  it  may  be  considered  a  "  levulo-glucoside, "  or  "levxilin." 
H  H 


H  H— C— O— H  H 

I  I  I 

H— O— C— H  H— C— O— H  H— O— C— H 

I                         I  I 
O— C— H  H— C— O— H  H— O— C— H 


H— O— C— H    =  H— C— O— H   +  H— O— C— H 


H— O— C— H 

C 


H— O— C— H 

I 
H 


Sucrose. 


H— C— O— H 

I 
H— C=0 


Dextrose. 


H— O— C— H 

I 

o=c 

I 
H— O— C— H 

I 
H 

Levulose. 


The  hydrogen  and  oxygen  of  water  enter  the  sucrose  molecule  as  indi- 
cated by  the  heavy  letters,  and  the  molecules  of  dextrose  and  levulose 
result. 


CA  RBOH  YDRA  TES  27 

ficially,  sucrose  can  be  hydrolyzed  by  boiling  with  a  dilute 
mineral  acid  like  hydrochloric,  the  products  of  this  acid 
hydrolysis  being  the  same  as  with  invertase.  The  mixture  of 
levulose  and  dextrose  thus  produced  is  known  as  invert  sugar, 
because  the  levorotatory  power  of  levulose  is  greater  than  the 
dextrorotatory  power  of  dextrose,  the  net  result  being  levo- 
rotation.  The  specific  rotation  of  invert  sugar  is  —20*.* 
Fungi  and  bacteria  containing  invertase  change  sucrose  to 
dextrose  and  levulose,  and  can  then  ferment  to  the  usual 
products  of  alcohol,  carbon  dioxide,  etc.  It  is  not  directly 
fermentable  in  most  cases. 

With  alkalies  and  alkaline  earths  sucrose  forms  saccha- 
rates,  or  "sucroxides,"  those  of  calcium  being  the  most  im- 
portant. There  are  three  compounds  with  calcium :  Mono- 
calcium  saccharate,  Ci2H2iOii.CaOH;  dicalcium  saccharate, 
Ci2H2oOu.2CaOH;  tricalcium  saccharate,  Ci2Hi90u.3CaOH. 
The  monocalcium  compound  is  readily  soluble  in  water,  the 
tricalcium  compound  difficultly  soluble.  The  latter  is  used 
commerically  in  the  separation  of  sucrose  from  beet  molasses. 
The  molasses  is  treated  with  freshly  burned  lime.  The 
resulting  precipitate  of  tricalcium  saccharate  is  filtered, 
washed  with  cold  water  and  decomposed  by  carbon  dioxide 
in  aqueous  suspension.    The  reaction  is  as  follows: 

CijHi»Oii.3CaOH  +  3C0j  =  CisHisOn  +  SCaCOa. 

Many  other  saccharates  are  also  formed,  such  as  those  of 
iron,  aluminium,  nickel,  and  copper.  Those  of  iron  are  used 
medicinally. 

Pure  sucrose  is  prepared  by  precipitating  it  from  a  solu- 
tion of  commercial  sucrose  with  cold,  absolute  alcohol,  and 

*  The  specific  rotation  of  levulose  is  —  92.5°  and  of  dextrose  is  +  52.5°,  but 
that  of  invert  sugar  is  not  —  40°,  but  —  20°,  since  specific  rotation  is  the 
angular  rotation  of  a  column  10  centimeters  long  which  contains  1  gram  of 
substance  in  1  cubic  centimeter  (footnote  p.  19),  and  1  gram  of  invert 
sugar  consists  of  i  gram  of  dextrose  and  i  gram  of  levulose,  thus  giving 
only  i  the  angular  difference  between  the  specific  rotations  of  levulose  and 
dextrose. 


28 


PLANT  COMPOUNDS 


washing  the  fine  crystals  with  absolute  alcohol.  Commercial 
sucrose  is  made  from  sugar  cane  by  squeezing  out  the  juice 
in  mills,  clarifying  with  lime  to  remove  impurities,  evapo- 
rating the  filtrate,  and  finally  crystallizing  out  the  sucrose. 
Fig.  4  shows  the  interior  of  a  sugar  factory  where  the  cane 
juice  is  being  evaporated.  Further  solution,  treatment 
with  lime  and  bone  black,  and  recrystallization  yields  the 
pure  granular  sugar  (sucrose)  of  commerce.     Brown  sugar 


Fig.  4. — Boiling  cane  juice  in  a  sugar  factory  at  Guadaloupe. 


is  obtained  by  evaporating  to  dryness  the  mother  liquor 
from  which  no  sucrose  will  crystallize.  Brown  sugar  origin- 
ally contained  some  caramel  because  the  evaporation  of  the 
syrup  was  carried  on  in  vats  heated  by  a  free  flame,  and  part 
of  the  material,  being  overheated,  caramelized.  Modern 
evaporators  are  steam-heated  vacuum  pans,  and  thus 
caramelization  is  avoided. 

From  the  sugar  beet,  sucrose  is  made  by  slicing  the  beets 
and  soaking  them  in  water,  thus  allowing  the  sucrose  to 


CARBOHYDRATES  29 

diffuse  gradually  out  of  the  beet  cells.  The  concentrated 
juice  is  clarified  and  purified  much  as  in  the  case  of  sugar 
cane  juice.  Beet  sugar  is  exactly  the  same  as  cane  sugar, 
although  when  first  made  methods  of  purification  were  not 
perfect,  and  the  admixed  impurities  made  its  quality  poorer 
than  that  of  cane  sugar. 

The  various  uses  of  cane  sugar  are  too  well  known  to 
need  description. 

6.  Maltose,  Maltobiose,  Malt  Sugar. — C12H22O11,  graphi- 
cally: 


H 


This  constitutes  another  double  "sugar"  group.  It  is 
one  of  the  most  widely  distributed  sugars  in  plants,  but 
since  it  is  never  a  storage  form  of  carbohydrates  it  is  not 
found  in  any  quantity,  as  are  the  other  sugars.  It  is  one 
of  the  transition  forms  from  starch  to  dextrose,  and  is 
formed  to  a  large  extent  in  the  germinating  seed  (Section  47). 
Of  itself,  however,  it  may  serve  as  a  transport  form  of 
carbohydrate  without  undergoing  a  change  to  dextrose. 
It  is  a  white,  crystalline  solid,  readily  soluble  in  water; 
slightly  soluble  in  cold  alcohol;  not  as  sweet  as  sucrose. 
It  is  dextrorotatory,  the  specific  rotation  being  +138°. 
Maltose  reduces  Fehling's  solution,  since  it  belongs  to  the 
aldehyde  group.  Under  the  action  of  an  enzyme  called  mal- 
tase,  it  is  hydrolyzed  to  dextrose,  one  molecule  of  maltose 


30  PLANT  COMPOUNDS 

breaking  up  into  two  molecules  of  dextrose.^  It  is  also 
hydrolyzed  to  dextrose  on  boiling  with  a  dilute  mineral  acid 
like  hydrochloric.  Maltose  ferments  only  as  it  is  hydro- 
lyzed to  dextrose  by  enzymes  (Section  46)  in  the  fungi  and 
bacteria.  It  forms  compounds  with  alkalies  and  alkaline 
earths,  but  they  are  of  no  importance. 

Maltose  is  prepared  by  treating  starch  paste  with  malt 
extract  (Section  47)  at  60°  C,  and  extracting  the  maltose  thus 
formed  with  successive  portions  of  hot  87  per  cent,  alcohol, 
finally  evaporating  and  allowing  it  to  crystallize.  It  is 
recrystallized  from  hot  methyl  alcohol,  after  purifying  with 
bone  black. 

Commercially  it  occurs  in  malt  and  malt  products  which 
are  made  from  germinating  barley  (Section  96,  a).  It  also 
occurs  mixed  with  dextrin  (Section  8)  as  a  thick  syrup  or 
solid.  In  a  rather  pure  form  as  a  syrup  it  is  used  to  some 
extent  as  a  substitute  for  cane  sugar,  particularly  during  the 
shortage  of  sugar  caused  by  the  Great  War. 

7.  Non-sugars  or  Polysaccharides. — ^These  compounds  are 
usually  colorless  or  white,  odorless,  and  amorphous,  with 
little  or  no  taste,  and  insoluble  in  water  and  in  alcohol. 
They  are  formed  by  the  condensation  of  a  great  many 
molecules  of  a  monosaccharide  with  the  elimination  of 
water,  thus: 

n  CeHnOs  —  n  H2O  =  (CeHioOs)  n. 

1  As  in  the  case  of  sucrose  this  hydrolytic  change  shows  the  glucoside-like 
character  of  maltose,  it  being  a  " gluco-glucoside, "  or  "glucolin."    Thus: 
H  H 

I  I 

H— C— O— H  0=C— H        H— C— O— H  0=C— H 

I  II  I 

H— C— O— H  H— O— C— H        H— C— O— H        H— O— C— H 

H— C— O 1         H— O— C— H   =  H— C— O— H  +  H— O— C— H 

I  I  I 

H— O— C— H        H— C— O— H        H— O— C— H 

I  I  I 

H— O— C— H        H— C— O— H        H— O— C— H 

I  I  I 

H— C O C— H        H— C  =0  H— O— C— H 

I  I 

H  H 

Maltose  Dextrose  Dextrose 


CARBOHYDRATES  31 

Each  molecule  consists  of  a  large  number  of  single  "sugar" 
groups.  Starch  and  cellulose  are  the  principal  polysac- 
charides. 

8.  Starch.  —  (C6Hio05)2oo(?).  The  exact  graphic  formula 
is  not  known.  Starch  occurs  in  all  parts  of  the  plant  as 
a  storage  form  of  carbohydrate  material,  being  a  condensed 
anhydride,  and  insoluble.  It  occurs  to  a  great  extent  in 
seeds  and  tubers  as  follows: 

Approximate  per  cent. 
Crops.  starch. 

Corn 62 

Wheat 64 

Oats 54 

Rice 70 

Potatoes 20 


Starch  occurs  in  plant  cells  in  the  form  of  very  small, 
white  grains,  the  size  and  shape  of  which  vary  with  the 
plant  which  manufactures  it.  Figs.  5  to  9  show  various 
kinds  of  starch  grains,  and  it  is  to  be  noted  that  those  of  the 
potato  are  comparatively  large,  while  those  of  rice  are  very 
small.  The  size  varies  from  about  0.002  mm.  to  0.2  mm.  in 
diameter.  These  grains  are  composed  of  very  thin  cellulose 
walls,  with  contents  of  powdery  material  called  granulose 
or  amylose.  They  are  insoluble  in  cold  water,  alcohol,  and 
ether,  but  on  treatment  with  boiling  water  the  cellulose 
envelope  ruptures  and  the  escaping  granulose  dissolves 
in  the  water  to  form  a  more  or  less  gelatinous  solution, 
slightly  cloudy  from  the  insoluble  cellulose  walls.  This 
semisolution  is  called  starch  paste.  It  is  strongly  dextro- 
rotatory, and  will  not  reduce  Fehling's  solution.  Its  most 
characteristic  reaction  is  to  turn  blue  in  the  cold  with  a 
solution  of  iodine  (in  alcohol  or  potassium  iodide).  The 
compound  formed  is  supposed  to  be  (C24H4o02oI)4.HI,  which 
breaks  up  on  heating,  but  which  reforms  again  when  the 
solution  is  cooled  down. 

Under  the  action  of  enzymes  (Section  46),  diastase  for 
example,  starch  hydrolyzes  to  maltose  (Section  6),  thus: 

2(C«HioO»)n  +  nHjO  =  nCiiHttOu. 


32 


PLANT  COMPOUNDS 


In  so  doing,  however,  it  passes  through  a  series  of  hydro- 
lytic  compounds,  named  successively:  Amylodextrin,  colored 


Fig.  5. — Potato  starch. 


Fig.  6. — Wheat  starch. 


CARBOHYDRATES 


33 


blue  by  iodine;  erythrodextrin,  colored  red  by  iodine;  achro- 
odextrin,  not  colored  by  iodine;  maltodextrin,  not  colored 


Fig.  7. — Corn  starch. 


Fig.  8.— Oat  starch. 


34 


PLANT  COMPOUNDS 


by  iodine;  maltose,  not  colored  by  iodine.  These  various 
dextrins  differ  from  starch  in  containing  a  smaller  number  of 
CeHioOs  groups  in  their  molecules.  They  are  colorless, 
soluble  in  water  to  a  gelatinous  consistency,  and  dextro- 
rotatory. They  can  also  be  made  from  starch  by  roasting 
it  in  ovens  with  about  0.2  per  cent,  nitric  acid  to  110°-170° 
C,  and  dissolving  out  the  so-called  Dextrin  or  British  Gum, 
which  is  used  in  the  textile  industries  for  thickening  colors, 
as  mucilage  on  stamps,  envelopes,  etc. 


Fig.  9. — Rice  starch. 

Figs.  5  to  9. — Starch  grains.      Bureau  of  Chemistry,  United  States 

Department  of  Agriculture. 


On  boiling  starch  with  mineral  acids  such  as  hydrochloric 
or  sulphuric,  the  same  hydrolytic  changes  take  place  except 
that  maltose  is  still  further  changed  into  dextrose.  If  starch 
is  treated  with  cold,  dilute  hydrochloric  acid  it  is  changed 
to  a  substance  called  soluble  starch,  which  is  probably  amylo- 
dextrin,  the  first  compound  formed  in  the  hydrolysis  of  starch. 
It  is  soluble  in  water  and  colored  blue  by  iodine. 

Commercial  starch  is  prepared  from  corn  by  grinding 
and  separating  the  starch  from  the  other  material  by  gravity 


CA  RBOH  YDRA  TES  35 

in  water;  from  potatoes  by  scraping  or  pulping,  filtering 
off  the  fiber,  and  washing  to  separate  the  starch.  It  is  used 
for  a  great  variety  of  purposes,  such  as  for  food  in  pud- 
dings, for  laundry  work,  for  sizing  in  paper  and  textiles, 
for  cosmetics,  etc. 

9.  Cellulose. — (CeHioOs),,  (n  greater  than  200).  The  graphic 
formula  is  not  well  understood,  but  the  following  has  been 
assigned  to  it  as  the  unit  group  which  occurs  a  large 
number  of  times: 

H  O— H     H  O— H 

\  /         \  / 

C C  H 

/  \  / 

O  =  C  C 

\  /   \ 

C C  H 

/    \  /   \ 

H  O— H     H  O— H 

Cellulose  comprises  about  one-half  of  the  dry  matter  of 
plants.^  It  forms  their  framework,  being  the  chief  con- 
stituent of  cell-walls  and  supporting  fibers.  Usually  it 
occurs  in  combination,  either  weakly  chemical  or  physical, 
with  so-called  "encrusting  substances"  derived  from  it, 
such  as  lignin  and  pentosans.  In  the  pure  form  it  occurs 
naturally  only  in  the  cotton  plant  as  a  mass  of  seed  hairs,  and 
in  a  very  few  other  plants.  It  is  derived  from  dextrose  by 
dehydration,  thus: 

nCHwOd  —  nHjO  =  (C«Hio06)n. 

Its  function  is  to  provide  a  somewhat  elastic,  but  fairly 
rigid  envelope  for  plant  cells.  Where  heavy  walls  are 
needed  and  heavy  weights  are  to  be  supported,  as  in  trees, 

•  Different  plant  materials  contain  the  following  approximate  amount 
of  cellulose: 

Per  cent. 

Wood 60 

Straw    . 40 

Seeds  (including  husks) 15 

Roots .,,,..,      10 


36  PLANT  COMPOUNDS 

these  walls  become  "lignified"  or  thickened,  filling  the  cell 
almost  completely.  This  thickened  part  forms  the  encrusting 
substances  mentioned  above. 

Physically,  cellulose  is  a  white,  amorphous  or  fibrous 
solid,  insoluble  without  decomposition  in  all  solvents. 
Cuprammonium  hydroxide  solution  (cf.  Section  204,  I,  c), 
called  Schweitzer's  reagent,  dissolves  cellulose  to  a  thick, 
viscous,  dark  blue  liquid  in  which  the  cellulose  exists  as  a 
complex  compound  with  the  copper  and  ammonia.  From 
this  solution  it  may  be  reprecipitated  in  the  amorphous 
form  by  acidification  with  hydrochloric  or  sulphuric  acid. 
A  strong  solution  of  zinc  chloride  in  concentrated  hydro- 
chloric acid  also  dissolves  cellulose  to  a  complex  compound 
from  which  it  may  be  recovered  on  treatment  with  alcohol. 
Cold,  concentrated  sulphuric  acid  dissolves  cellulose.  In 
so  dissolving  it  is  changed  to  a  cellulose  sulphuric  acid 
compound  from  which  the  cellulose  can  not  be  recovered. 
On  diluting  such  a  solution  and  boiling  it,  the  cellulose  is 
hydroly zed  to  dextrose. 

If  cellulose  is  treated  with  a  cold  solution  of  sodium 
hydroxide  stronger  than  10  per  cent.,  a  compound  is  formed 
which  has  a  formula  something  like  this:  CeHgOsNa.  On 
washing  with  water  the  cellulose  is  regenerated  as  the  hydrate, 
(C6Hio05)2-H20.  If  cotton  cloth  is  stretched  on  a  frame  and 
treated  in  this  way  there  is  obtained  a  cloth  of  silky  appear- 
ance called  "mercerized  cotton.'  The  treatment  results 
in  a  shrinking  of  the  cotton  fibers,  and  a  resultant  gloss  if 
the  cloth  is  kept  taut  during  the  shrinking  process. 

If  the  above  mentioned  soda-cellulose  is  treated  with 
carbon  disulphide  a  compound  is  formed  called  "viscose," 

O— C.H.O4 

/ 
s=c 

\ 

S— Na 

which  is  soluble  in  water  to  a  viscous  liquid.  On  spon- 
taneous decomposition  in  the  air,  viscose  loses  carbon 
disulphide  and  sodium  hydroxide.     The  former  disappears 


CARBOH  YDRA  TES  37 

by  volatilization  and  the  latter  may  be  washed  out.  A 
hard,  transparent,  vitreous  mass  of  cellulose  is  left.  This 
is  called  "viscoid"  or  "cellophane"  and  finds  a  variety  of 
uses.  On  treating  cotton  with  nitric  and  sulphuric  acids 
there  are  obtained,  according  to  conditions,  a  trinitrate 
of  cellulose,  C6Hio05(N03)3,  or  a  dinitrate  of  cellulose, 
C6Hio06(X03)2-  The  former,  insoluble  in  alcohol  and  ether, 
is  known  as  guncotton,  the  explosive;  the  latter,  soluble  in 
alcohol  and  ether,  is  called  pyroxylin  or  soluble  cotton.  The 
solution  of  pjToxylin  in  alcohol  and  ether  is  known  as  collo- 
dion which  finds  a  variety  of  uses  in  surgery  as  a  dressing  for 
wounds,  and  in  photography  for  making  films.  If  pyroxylin 
is  intimately  mixed  with  camphor,  celluloid  results. 

The  thick  viscous  solutions  of  cellulose  in  ammoniacal 
cupric  hydrate,  of  viscose,  and  of  collodion,  all  serve  as 
materials  for  making  artificial  silk.  By  squeezing  the  thick 
liquid  through  exceedingly  fine  holes,  and  winding  the 
resulting  filaments  into  a  thread,  a  lustrous  imitation  silk 
is  made  after  regenerating  the  cellulose.  In  the  case  of  the 
ammoniacal  copper  hydrate  solution  the  cellulose  is  formed 
by  treating  the  threads  with  dilute  sulphuric  acid  and 
washing;  in  the  case  of  viscose,  by  simple  drying  and  wash- 
ing; and  in  the  case  of  collodion  by  denitrating  with  alkaline 
sulphides. 

Under  proper  conditions  cellulose  will  unite  with  acetic 
acid  to  form  a  tetra-acetate  CeHeO (€211302)4,  soluble  in 
nitrobenzol.  On  evaporation  of  the  solvent  there  is  formed 
a  transparent  film  that  is  used  for  photographic  purposes. 
It  is  also  a  superior  insulating  material  for  electric  wires. 

From  the  above  discussion  it  can  be  seen  that  cellulose 
has  both  acid  and  basic  properties,  since  it  forms  compounds 
with  bases  like  sodium  and  copper  hydroxides,  on  the  one 
hand,  and  with  nitric  and  acetic  acids,  on  the  other.  On 
the  whole,  however,  it  is  exceedingly  inert,  resisting  all 
ordinary  decomposition  and  decay.  It  is  not  fermentable. 
It  finds  its  chief  use  on  account  of  this  decay-resistant 
property  in  the  manufacture  of  rope,  cotton  cloth,  linen 
cloth,  paper,  and  other  articles,  all  of  which  are  made  of 
cellulose  from  different  sources. 


38 


PLANT  COMPOUNDS 


Cotton  fiber  (Fig.  10)  is  the  purest  form  of  cellulose, 
but  even  that  must  be  treated  with  alkali,  acid,  alcohol,  and 
ether  to  remove  impurities  attached  to  it,  such  as  proteins 
and  fats.  In  the  case  of  flax  used  for  linen,  and  hemp  used 
for  rope,  various  processes  are  employed  to  free  the  crude 
cellulose  fibers  from  their  encrusting  substances.  In  making 
paper  from  wood,  the  lignin  and  other  impurities  are  dis- 
solved away  by  a  weak  caustic  soda  solution  (Soda  Process), 
or  an  acid  sulphite  solution  (Sulphite  Process).  The  remain- 
ing cellulose  fibers,  which,  by  the  way,  are  much  shorter 


Fig.  10. — Cotton  fiber.    Magnified,    Drawing  by  C.  A.  Smith. 


than  cotton  and  linen  fibers,  are  sized,  loaded,  and  matted 
into  paper  of  various  kinds.  If  unsized  paper,  that  is, 
pure,  matted,  cellulose  fibers,  are  dipped  in  fairly  strong 
sulphuric  acid  for  an  instant  and  then  plunged  into  water, 
the  cellulose  assumes  a  tough,  parchment-like  texture,  and 
is  used  as  a  substitute  for  sheepskin.  This  material  is  called 
"amyloid,"  since  it  is  starch-like  in  character,  giving  a  blue 
color  with  iodine. 

10.      Lignin    and    Pentosans. — These    "encrusting  sub- 
stances" are  derived  from  cellulose  apparently,  but  differ 


CA  RBOH  YDRA  TES  39 

from  it  in  chemical  composition.  Lignin  contains  less  oxygen 
than  cellulose,  and  in  addition  contains  methyl  (CH3)  groups. 
It  is  soluble  with  decomposition  in  hot  dilute  alkali,  acid 
sulphite,  and  some  other  solvents.  It  is  easily  decomposed 
by  chlorine  and  bromine.  It  forms  a  large  part  of  the  woody 
fiber  of  trees,  and  hence  its  name,  lignin.  Pentosans  are 
compounds  of  the  general  formula  (C5H804)n  which  are 
hydrolyzed  by  acids  to  pentoses,  C5H10O5.  Xylan  and  araban, 
hydrolyzing  to  xylose  and  arabinose,  are  examples.  Pento- 
sans form  some  10  per  cent,  of  the  dry  matter  of  coniferous 
trees  and  20  per  cent,  of  deciduous  trees. 

11.  Inulin. — (C6Hio05)6.  This  carbohydrate  occurs  natur- 
ally as  a  storage  form  of  carbohydrate  in  the  roots  of  such 
plants  as  dandelion,  dahlia,  and  chicory.  It  is  derived 
undoubtedly  as  are  the  other  anhydride  forms  of  dextrose 
by  a  dehydration  process:  6C6H12O6— 6H20=(C6Hio06)6.  It 
is  a  white,  crystalline  substance  easily  soluble  in  water, 
insoluble  in  alcohol.  It  does  not  reduce  Fehling's  solution, 
and  is  levorotatory.  It  hydrolyzes  under  the  action  of 
dilute  mineral  acids  and  of  the  enzyme  (Section  46),  inulase, 
to  levulose.    It  is  not  fermentable. 

12.  Gums. — These  are  amorphous  substances  of  unknown 
composition,  but  are  probably  glucosides  of  organic  acids. 
They  are  soluble  in  water,  or  at  least  gelatinize  in  it,  insoluble 
in  alcohol,  and  hydrolyze  with  acids  to  hexoses  and  pentoses. 
Gum  arable,  used  in  making  mucilage,  and  various  wood 
gums,  are  examples. 

13.  Pectins. — Pectins  are  amorphous,  white  substances 
found  in  most  fruit  juices,  soluble  in  water,  but  insoluble 
in  alcohol.  They  are  related  to  the  gums  and  are  probably 
carbohydrates.  By  enzyme  action  (Section  46)  they  are 
derived  from  insoluble  pectose  which  gives  hardness  to  unripe 
fruit.  The  pectins  in  turn  are  changed  to  pectic  acid  by 
enzymes  (Section  46)  as  the  fruit  ripens,  and  the  calcium  salt 
of  pectic  acid  is  what  makes  the  juice  of  fruits  like  apples, 
plums,  and  grapes,  solidify  to  a  jelly. 


40  PLANT  COMPOUNDS 


n.     FIXED  OILS  AND  WAXES 

14,  General  Definition. — ^The  name  oil  is  given  to  liquid 
substances  which  are  characterized  by  their  slippery  or 
greasy  feel,  and  by  the  fact  that  they  leave  a  grease  spot, 
or  permanent  translucent  spot  on  paper.  These  properties 
are  the  same  whether  the  oils  are  the  so-called  mineral 
oils,  hydrocarbons  occurring  naturally  in  the  earth,  or  are 
vegetable  oils,  called  fixed  oils  or  fats,  or  are  volatile  oils 
also  found  in  plants. 

The  fixed  oils  are  always  esters  of  glycerine  and  fatty  acids, 
or  glycerides  of  fatty  acids.  Glycerine  being  a  trihydric 
alcohol  can  combine  with  one,  two,  or  three  monobasic 
fatty  acids,  and  most  fixed  oils  are  mixtures  of  compounds 
of  glycerine  with  more  than  one  fatty  acid.  The  name  oil 
usually  signifies  a  liquid  compound,  fat  being  the  name 
usually  given  to  a  fixed  oil  which  is  solid  at  ordinary  tempera- 
tures. When  found  in  plants  the  fixed  oils  are  sometimes 
called  vegetable  oils  to  distinguish  them  from  the  so-called 
animal  oils  which  are  found  in  animals.  The  present  dis- 
cussion will  be  confined  to  fixed  oils  of  plants,  or  vegetable 
oils,  although  the  general  characteristics  are  the  same  for 
both  classes  of  fixed  oils. 

15.  Properties. — Fixed  oils  when  pure  are  colorless  or 
pale  yellow.  When  impure  they  are  frequently  darker  in 
color,  sometimes  even  greenish  in  shade  from  the  presence 
of  small  amounts  of  chlorophyl.  With  few  exceptions  they 
have  no  particular  odor  or  taste.  They  are  lighter  than 
water,  their  specific  gravity  varying  from  0.875  to  0.970. 

They  will  not  distill  unchanged.  On  heating  they  de- 
compose into  various  compounds  depending  on  the  tem- 
perature. They  are  insoluble  in  water  and  in  cold  alcohol, 
somewhat  soluble  in  hot  alcohol,  easily  soluble  in  ether, 
chloroform,  carbon  tetrachloride,  carbon  disulphide,  and 
other  volatile  solvents.  They  "saponify"  on  treatment  with 
alkaline  hydroxides,  that  is,  they  break  up  into  glycerine 
and  the  alkaline  salt  of  the  fatty  acid,  called  a  soap  (Section 
17).    They  hydrolyze  to  glycerine  and  fatty  acids  on  treat- 


FIXED  OILS  AND  WAXES  41 

ment  with  steam,  and  also  under  the  influence  of  lipases 
(Section  48). 

They  are  found  for  the  most  part  in  the  seeds  of  plants, 
where  they  serve  as  reserve  material  for  respiration,  or  from 
which  to  make  carbohydrates  (Sections  48  and  71 ) .  Fixed  oils 
are,  however,  found  in  all  living  cells  of  plants  and  apparently 
play  a  necessary  part  in  the  functioning  of  protoplasm. 

The  fixed  oils  are  "drying"  or  "non-drying"  in  character. 
That  is,  on  exposure  to  the  air  some  of  them  absorb  oxygen 
and  harden  more  or  less,  while  others  remain  perfectly  liquid. 
This  is  a  property  of  the  fatty  acid  radicle.  The  non-drying 
oils  on  exposure  to  the  air  slowly  become  rancid,  that  is, 
oxidation  takes  place,  helped  by  the  action  of  bacteria,  which 
gives  the  oils  a  disagreeable  smell  and  taste,  and  makes  them 
acid  to  litmus.  This  is  caused  by  the  formation  of  free  fatty 
acids  with  some  other  products. 

16.  Methods  of  Extraction. — ^An  old  way  of  extracting 
fixed  oils  from  seeds  and  other  plant  substances  was  to  crush 
them  and  boil  with  water.  The  oil  rising  to  the  top  could 
be  skimmed  off.  Another  way  is  to  extract  the  oil  with 
volatile  solvents  which  can  later  be  distilled  off,  leaving  the 
oil  behind.  This  process,  however,  is  expensive  and  the 
product  contains  other  compounds  which  dissolve  out  in 
the  solvent  and  remain  as  impurities  in  the  oil. 

The  most  common  method  is  to  clean  and  decorticate  the 
seeds,  place  them  in  bags  and  squeeze  the  oil  out  by  heavy 
presses.  The  first  expression  is  made  in  the  cold  which  gives 
a  better  quality  of  oil.  The  pulp  is  then  expressed  hot  and 
more  oil  is  obtained,  but  it  is  not  so  pure.  The  material 
remaining  is  called  "press  cake,"  and  when  ground  is  sold 
for  cattle  food  and  fertilizers. 

17.  Soap. — The  saponifying  property  of  fixed  oils  is 
made  use  of  in  the  manufacture  of  soap.  If  potassium 
hydroxide  is  used  a  soft  soap  results,  if  sodium  hydroxide, 
a  hard  soap.  Both  kinds  are  soluble  in  water,  but  the  potash 
salt  of  the  fatty  acids  is  a  soft  substance,  whereas  the  soda 
salt  is  a  hard  substance.  The  oil  or  fat  is  boiled  with  the 
alkali  until  saponification  is  complete.  If  a  hard  product 
is  being  made,  the  soap  is  separated  from  the  resulting 


42  PLANT  COMPOUNDS 

glycerine  and  the  excess  of  alkali  by  the  addition  of  common 
salt.  The  soap  is  insoluble  in  this  solution,  and  can  be 
separated,  further  treated,  and  made  into  cakes. 

18.  Glycerine. — From  the  residue  after  the  removal  of 
soap,  glycerine  may  be  obtained  by  special  processes  in- 
cluding purification  by  distillation  under  reduced  pressure. 
Glycerine  is  a  thick,  oily  liquid,  hygroscopic,  miscible  with 
water  in  all  proportions,  and  has  a  very  sweet  taste.  Its 
formula  is  C3H5(OH)3,  graphically: 

H 

I 

H— C— O— H 

I 
H— C— O— H 

I 
H— C— O— H 

I 
H 

It  is  used  in  the  manufacture  of  nitroglycerine  and  dyna- 
mite; as  a  solvent  in  confectionery  on  account  of  its  hygro- 
scopic qualities  which  keep  candy  soft;  in  printing  inks,  etc. 

19.  Classification  of  the  Fatty  Acids. — ^The  drying  property 
of  oils  depends  on  the  existence  of  double  bonds  in  the  fatty 
acid  radical ;  or  to  express  it  in  another  way,  on  the  existence 
of  unsaturated  carbon  atoms  which  readily  take  up  oxygen. 
On  this  basis  the  fatty  acids  of  the  fixed  oils  may  be  classified 
as  saturated  or  unsaturated  compounds  as  follows: 

(a)  Saturated  Fatty  Acids. — CnH2n+iC00H.  Stearic 
acid,  C17H35COOH,  melting  point  69°  C. 

CH3.(CH2)i6.COOH 

Palmitic  acid,  C15H31COOH,  melting  point  62°  C. 

CHs.(CH2)i4.COOH 

(6)  Unsaturated  Fatty  Acids. — (1)  With  one  double  bond, 
CnHan-iCOOH.  Oleic  acid,  C17H33COOH,  melting  point  14°  C. 

CH».(CH2)7.CH:CH.(CH2)7.COOH 

(2)  With  two  double  bonds,  CnH2n-3COOH.  Linoleic  acid, 
C17II31COOH,  melting  point  below- 18°  C. 

CH».(CH2)«.CH:CH.CH:CH.(CH2)«.COOH 


FIXED  OILS  AND   WAXES  43 

(3)  Wifh  three  double  bonds,  CnHan-sCOOH.  Linoleic 
acid,  Ci7H29CC)OH,  liquid  at  ordinary  temperatures. 

CHi.(CH,)».CH:CH.CH:CH.CH:CH.(CH.)».COOH 

The  presence  of  more  than  one  double  bond  in  the  fatty 
acid  is  necessary  for  a  true  drying  oil  of  commercial  value. 
One  double  bond  in  the  acid  radical  does  not  allow  enough 
oxygen  to  be  absorbed — does  not  harden  sufficiently. 

The  glycerides  are  named  according  to  the  fatty  acid 
radical,  thus:  Olein  for  a  glyceride  of  oleic  acid,  palmitin, 
for  one  of  palmitic  acid,  stearin  for  one  of  stearic  acid,  etc. 

In  the  above  classification  it  is  to  be  noted  that  palmitic 
and  stearic  acids  are  solid  at  ordinary  temperatures,  and 
oils  containing  a  large  proportion  of  these  acids  are  solid 
at  ordinary  temperatures.  They  are  called  fats.  The  other 
acids  mentioned  are  liquid  at  ordinary  temperatures  and  oils 
containing  them  are  usually  liquid.  This  property  of  being 
solid  is  more  or  less  characteristic  of  the  saturated  group, 
and  of  being  liquid  more  or  less  characteristic  of  the  unsatu- 
rated group,  although  not  exclusively  so.  Some  acids  of  the 
first  group  are  liquid  at  ordinary  temperatures,  and  some 
acids  of  the  second  group  are  solid. 

In  most  cases  the  plant  fixed  oils  are  liquid  and  contain 
a  larger  proportion  of  the  liquid  fatty  acids  than  do  animal 
fixed  oils  which  are  called  fats.  The  latter  contain  as  a 
rule  more  stearic  and  palmitic  acids. 

Oils  containing  oleic  acid  have  a  slight  drying  power. 
Those  containing  linoleic  and  linolenic  are  much  better 
"driers."  The  "drying,"  it  should  be  remembered,  is  an 
oxidation  process,  resulting  in  the  formation  of  a  hard,  resin- 
ous compound,  and  not  a  desiccation  which  is  the  case  in 
true  drying.  Non-drying  oils  may  be  used  as  lubricants, 
but  drying  oils  are  not  suited  for  this  purpose,  since  the 
"drying"  would  make  them  lose  their  lubricating  qualities. 

20.  Some  Common  Fixed  Oils. — (a)  Castor  Oil  is  a  thick, 
viscous,  transparent,  colorless  or  slightly  yellow  oil  of  dis- 
agreeable taste.  It  is  pressed  from  the  seeds  of  the  castor 
bean  which  contain  about  50  per  cent,  of  oil,  and  is  composed 
of  small  amounts  of  stearin  but  principally  of  ricinolein,  the 


44  PLANT  COMPOUNDS 

latter  being  the  glyeeride  of  ricinoleic  acid,  a  hydroxy-acid 
with  one  double  bond,  C17H32OH.COOH.  It  is  used  in 
medicine;  for  making  soap;  and  as  a  lubricant  for  heavy 
machinery,  since  it  is  very  viscous  and  does  not  "dry" 
appreciably. 

(b)  Corn  Oil  is  a  pale  yellow,  fluid  oil,  with  a  smell  of 
corn  meal.  It  is  composed  mostly  of  olein  and  linolein 
and  is  a  semi-drying  oil.  It  is  derived  by  pressing  the  germs 
which  have  been  removed  from  corn  kernels  previous  to 
the  manufacture  of  starch  (Fig.  19).  It  is  used  largely  in 
making  soap,  oil-cloth,  and  as  an  adulterant  of  edible  oils. 
The  press  cake  is  an  excellent  cattle  food. 

(c)  Cottonseed  Oil,  when  purified,  is  a  straw  colored, 
pleasant  tasting  oil,  composed  of  palmitin,  stearin,  olein, 
and  linolein.  It  is  made  from  husked  or  decorticated  cotton 
seeds  by  pressure  when  hot,  and  the  resulting  oil,  18  per  cent, 
yield,  is  clarified.  By  cooling  below  12°  C.  the  solid  fats, 
palmitin  and  stearin,  separate  out  and  can  be  obtained  by 
pressing.  "Cottonseed  stearin"  is  used  in  making  butter 
substitutes,  such  as  oleomargarine.  The  original  oil  is  used 
as  a  substitute  for  olive  oil  and  to  adulterate  olive  oil, 
but  principally  in  soap  making.  The  press  cake  is  used  for 
cattle  food. 

(d)  Linseed  Oil  is  obtained  by  cold  pressing  or  hot  press- 
ing the  seeds  of  the  flax  plant  (Fig.  26  shows  a  field  of  flax 
in  blossom).  The  seeds  contain  from  30  to  40  per  cent,  of 
oil.  The  cold  pressed  product  is  clear  and  yellow,  containing 
less  solid  glycerides  and  hence  is  a  better  drying  oil.  It 
is  also  used  as  a  food  in  some  countries,  whereas  the  hot 
pressed  oil  is  brown  and  unfit  to  use  as  a  food.  The  pressed 
oil  is  allowed  to  stand  for  some  time  to  allow  impurities  to 
settle,  and  it  is  also  further  purified  and  bleached.  It  contains 
about  58.5  per  cent,  isolinolenin  (isolinolenic  acid  has  the 
same  empirical  formula  as  linolenic  acid,  but  a  different 
structural  formula),  13.5  per  cent,  linolein,  13.5  per  cent, 
linolenin,  4.5  per  cent,  olein,  and  10  per  cent,  of  solid  glycer- 
ides, stearin,  palmitin,  and  myristin  (from  myristic  acid, 
saturated,  C13H27COOH). 

Linseed  is  the  principal  drying  oil  and  has  been  used  for 


FIXED  OILS  AND  WAXES  45 

hundreds  of  years  in  the  paint  and  varnish  industry.  Its 
usefulness  lies  in  the  fact  that  a  thin  layer  of  it  dries  or 
oxidizes  to  a  hard,  transparent,  more  or  less  glossy  skin 
which  serves  as  varnish  when  uncolored  or  as  a  paint  when 
mixed  with  pigments.  If  linseed  oil  is  boiled  first  it  dries 
more  quickly  on  exposure  to  the  air.  Also  if  the  oil  is  boiled 
with  "driers"  such  as  lead  oxide,  lead  resinate,  manganese 
borate,  and  manganese  resinate,  the  drying  process  is 
hastened,  probably  by  the  metallic  salts  acting  as  catalytic 
agents  in  the  oxidation.  Raw,  or  unboiled  oil  is  used  for 
making  soap,  some  kinds  of  paints  and  varnishes,  and  for 
rubber  substitutes  by  "vulcanizing"  with  sulphur  or  sulphur 
monochloride.  The  boiled  oil  is  used  for  paints,  printer's 
inks,  oil-cloth,  linoleum,  etc. 

The  oxidation  process  which  drying  oils  undergo  develops 
considerable  heat.  Cotton  waste  or  similar  material  soaked 
in  linseed  oil  has  been  known  to  take  fire  spontaneously,  the 
loose  mass  of  material  preventing  the  radiation  of  the  heat 
which  gradually  increases  to  the  "flash  point." 

Press  cake  from  hot  pressed  linseed  oil  makes  an  excellent 
cattle  food.  The  cold  pressed  cake  is  more  apt  to  poison 
cattle  because  of  the  presence  of  a  hydrocyanic  acid  glucoside 
which  is  acted  upon  by  an  enzyme  (Section  46)  in  the  presence 
of  water  with  consequent  hydrolysis  to  hydrocyanic  acid  and 
glucose.  The  former  is  the  poison.  Hot  pressed  cake  on  the 
other  hand  has  had  the  enzjine  destroyed  by  heat  and  no 
hydrolytic  action  takes  place,  the  glucoside  itself  being 
harmless. 

(e)  Olive  Oil  is  made  by  pressing  the  fruit  pulp  and  the 
seeds.  The  cold  pressed  oil  from  the  former  is  the  better 
grade  and  is  employed  as  a  condiment.  The  oil  expressed  hot 
from  the  original  cake  and  from  the  seeds  is  less  pure  and  is 
used  for  lubricating  purposes  and  soap  making.  The  color 
of  the  oil  varies  from  a  pale  yellow  to  a  greenish  or  brownish 
shade.  It  contains  about  72  per  cent,  olein  and  28  per  cent, 
palmitin.  Thin  films  dry  slowly.  Cotton  seed  oil  is  the 
principal  adulterant. 

(/)  Peanut  Oil  is  obtained  from  peanuts,  and  is  a  light 
greenish-yellow  oil,  although  colorless  when  refined.     It  is 


46  PLANT  COMPOUNDS 

used  as  an  adulterant  for  olive  oil,  as  a  salad  oil  under 
its  own  name,  and  for  making  butterine  and  soap.  It  con- 
tains olein,  linolein,  palmitin,  stearin,  and  some  less  known 
glycerides. 

(g)  Rapeseed  Oil  or  Colza  Oil  is  obtained  from  rapeseed 
by  hot  pressing.  The  purified  oil  is  light  colored  and  used 
as  a  condiment  under  the  name  of  colza  oil,  rape  seed  oil 
being  applied  to  the  darker  colored  oil  which  is  used  as  a 
lubricant  and  to  some  extent  as  a  burning  oil.  Both  kinds, 
containing  mostly  olein,  stearin,  and  brassin,  are  very 
viscous,  and  on  exposure  to  the  air,  become  gummy,  but 
do  not  dry. 

(h)  Sunflower  Oil  is  obtained  from  the  seeds  of  the 
sunflower.  It  is  pale  yellow  and  of  pleasant  taste,  being 
used  in  cooking.  Less  pure  grades  are  used  for  soap  making 
and  as  an  adulterant  for  linseed  oil,  although  it  does  not  dry 
as  quickly.  It  is  composed  principally  of  olein,  palmitin  and 
linolein. 

21.  Waxes. — These  compounds  are  allied  to  the  fixed 
oils  in  that  they  have  many  of  the  properties  of  oils,  and  are 
esters  of  fatty  acids,  but  the  acids  are  combined  with  mono- 
hydric  alcohols  of  high  molecular  weight,  and  not  with 
glycerine.  In  the  plant  they  serve  as  a  protective  water- 
proof coating  on  the  stems,  leaves,  and  fruit  of  many  plants. 
The  "bloom"  on  plums  is  a  wax.  The  surface  of  corn  stalks 
and  sugar  cane  is  covered  with  a  thin  layer  of  wax.  The 
waxes  may  be  liquid  or  solid  and  are  found  in  animals  as 
well  as  in  plants. 

Carnauba  Wax  is  the  principal  plant  wax.  It  ife  a  very 
hard  substance,  usually  of  sulphur  yellow  color  and  obtained 
from  the  leaves  of  a  certain  kind  of  palm  tree  in  Brazil  by 
scraping  the  surface  of  the  leaves,  melting  and  collecting  it 
in  boiling  water.  It  contains  an  ester  of  so-called  myricyl 
alcohol,  CsoHeiOH,  and  cerotic  acid,  C25H61COOH,  and  some 
other  similar  esters.  It  is  used  in  making  candles,  polishing 
pastes,  and  phonograph  cylinders. 

22.  Lecithin. — While  this  compound  is  not  a  wax  or  fat, 
it  is  allied  to  them  in  chemical  composition.    It  is  an  ester 


VOLATILE  OILS  AND  RESINS  47 

of  glycerine  and  choline  with  fatty  acids   and   phosphoric 

acid.    Its  formula  may  be  as  follows: 

H 

I 

:.H»CiT 

HnCu 


Cm.CHi.N  i  (CHi)i 

I 
OH 

This  would  be  called  a  stearo-palmito-phosphate  of  glycerine 
and  choline.  Other  fatty  acids  may  replace  the  two  given. 
It  is  a  yellowish-white,  waxy  substance,  soluble  in  alco- 
hol, and  other  organic  solvents.  In  water  it  forms  an 
opalescent  emulsion  or  solution.  Since  it  contains  certain 
fat  radicals,  a  reduced  nitrogen  group,  and  phosphoric  acid, 
it  may  be  useful  in  the  formation  of  fats  or  of  proteins.  It 
is  found  in  cereal  grains,  peas,  and  beans,  to  a  larger  extent 
than  in  other  plants,  although  present  in  most  plant  cells. 

m.    VOLATILE  OILS  AND  RESINS 

23.  General  Definition. — The  name  oil  signifies  a  liquid 
having  certain  characteristic  properties  as  noted  in  Section 
14,  but  the  volatile  oils,  also  called  essential  or  ethereal  oils, 
are  less  greasy  in  character  than  the  fixed  oils,  and  are 
volatile  on  exposure  to  the  air;  so  that  the  spot  they  leave 
on  paper  will  disappear  in  time.  Chemically  they  are  of 
several  different  kinds  of  compounds,  to  be  noted  later 
(Section  26).  They  are  to  be  found  free  or  as  glucosides 
in  all  parts  of  plants,  except  in  the  seeds  where  the  fixed 
oils  predominate.  The  glucosides  hydrolyze  under  certain 
conditions  with  the  help  of  enzymes  to  glucose  and  the 
volatile  oil.  The  volatile  oils  apparently  serve  no  true 
physiological  function  in  plants,  being  for  the  most  part 
by-products  or  end-products  in  metabolism.  They  frequently 
serve  as  valuable  helps  to  the  plant,  however,  in  attracting 
insects  whereby  fertilization  is  effected;  or  as  repellents 
to  keep  off  harmful  insects. 


48  PLANT  COMPOUNDS 

24.  Properties. — Volatile  oils  are  usually  colorless  or 
yellow  when  fresh,  but  darken  on  standing.  They  have  very 
characteristic  odors  and  tastes  and  are  valuable  commercially 
for  these  properties.  Most  of  them  are  lighter  than  water, 
varying  in  specific  gravity  from  0.850  to  0.990,  although  a 
few  are  less  than  0.850  and  many  of  the  more  common  oils 
are  heavier  than  water.  They  will  for  the  most  part  distill 
unchanged,  especially  under  reduced  pressure.  They  are 
slowly  volatile  at  ordinary  temperatures,  hence  the  dis- 
tinction in  names  between  the  fixed  oils,  which  are  not 
volatile,  and  the  volatile  oils,  which  are  like  their  name. 
Their  boiling  points  are  rather  high.  Volatile  oils  are 
insoluble  in  water,  although  many  of  them  dissolve  to  a 
slight  extent,  imparting  the  characteristic  odor  and  taste 
to  the  water.  They  are  readily  soluble  in  cold  alcohol  as 
well  as  in  hot  alcohol,  and  in  ether,  chloroform,  carbon 
tetrachloride,  and  carbon  disulphide.  They  are  also  mis- 
cible  in  all  proportions  with  fixed  oils.  Only  those  which  are 
esters  saponify. 

25.  Methods  of  Extraction. — ^There  are  several  ways  of 
obtaining  the  volatile  oils  for  commercial  use : 

(a)  By  Expression,  very  much  as  in  the  case  of  the  fixed 
oils. 

(b)  By  Distillation  with  Water  or  Steam  whereby 
the  crushed  material  to  be  extracted  is  either  boiled  with 
water  or  has  a  current  of  steam  passed  through  it.  The 
volatile  oil  is  carried  over  with  the  steam  and  condensed. 
The  oil  and  water  can  easily  be  separated  because  of  their 
insolubility  in  each  other  and  because  of  the  difference  in 
their  specific  gravities. 

(c)  By  Hydrolysis  and  Distillation. — Some  oils  occur 
as  glucosides  not  only  of  the  oil  but  also  of  other  compounds. 
Occurring  with  them  in  the  plant  is  an  enzyme  which  under 
favorable  conditions  of  moisture  and  temperature  acts  on  the 
glucosides,  forming  in  addition  to  glucose  the  volatile  oil 
and  the  other  compound  if  it  is  present.  Commercially  the 
oil  is  obtained  by  crushing  the  material  in  water,  allowing 
the  enzyme  to  act,  and  distilling  off  the  oil. 


VOLATILE  OILS  AND  RESINS  49 

(d)  By  Solution  in  a  Fixed  Oil,  such  as  olive  oil  or  lard. 
The  product  is  used  as  a  perfumed  oil  or  an  unguent. 

(e)  By  Extraction  with  a  Solvent  much  more  volatile 
than  the  oil.  The  solvent  is  removed  by  distillation.  This 
method  is  applicable  only  for  such  oils  as  have  high  boiling 
points. 

26.  Classification. — The  volatile  oils  as  obtained  from 
plants  are  not  single  chemical  compounds,  but  are  very 
frequently  mixtures  of  several  chemical  individuals,  and  the 
difficulty  often  experienced  in  obtaining  an  extracted  oil 
which  resembles  the  original  is  due  either  to  a  failure  to 
obtain  every  compound,  or  to  obtain  them  in  the  proper 
proportions.  Each  oil,  however,  generally  contains  one 
principal  con\pound  to  which  are  due  most  of  the  odor  and 
taste.  For  convenience,  these  compounds  may  be  classified 
into  three  groups: 

(a)  Carbon-Hydrogen  Compounds. — ^These  constituents 
belong  to  that  class  of  hydrocarbons  called  terpenes — ring 
compounds  which  have  a  general  formula,  CioHie,  or  a  mul- 
tiple thereof.  They  may  be  terpenes  proper,  CioHie,  or. 
sesquiterpenes,  C15H24. 

(6)  Carbon-Hydrogen-Oxygen  Compounds.  —  These 
constituents  may  be  alcohols,  aldehydes,  or  ketones  of  the 
aliphatic  or  carbocyclic  series,  or  esters  of  any  of  the 
alcohols  and  acids. 

(c)  Carbon-Hydrogen-Sulphur  Compounds. — In  addi- 
tion these  compounds  sometimes  contain  nitrogen.  They  are 
usually  organic  sulphides,  or  thiocyanates.  The  constitu- 
ents containing  oxygen  or  sulphur  have  much  stronger  odors 
and  flavors  than  the  terpenes,  and  are  more  useful  for  these 
properties  than  are  the  commoner  terpenes. 

27.  Some  Common  Volatile  Oils. — (a)  Oil  of  Bitter 
Almonds. — This  oil  is  benzaldehyde,  CeHoCHO,  occurring  in 
the  almond  kernel  as  a  glucoside  of  hydrocyanic  acid  and  ben- 
zaldehyde, called  amygdalin.  The  fixed  oil  is  first  expressed, 
and  the  cake  is  crushed,  soaked  in  water  until  the  enzyme, 
emulsin,  hydrolyzes  the  glucoside  to  benzaldehyde,  hydro- 
cyanic acid,  and  dextrose.     The  mixture  is  then  distilled. 

Hydrocyanic  acid  is  a  very  powerful  poison  and  care  must 

4 


50  PLANT  COMPOUNDS 

be  taken  in  the  distillation.  Moreover,  the  distillate  must 
be  carefully  freed  from  hydrocyanic  acid  before  use.  Apricot 
and  peach  seeds  also  contain  amygdalin  and  most  of  the 
commercial  oil  of  bitter  almonds  is  obtained  from  the  former. 
It  is  a  white  liquid  when  pure,  heavier  than  water,  and  is 
used  in  making  dyes  and  for  flavoring  purposes. 

(6)  Oil    of    Cinnamon.  —  This    oil  consists    mostly    of 
cinnamic  aldehyde  and  eugenol,  represented  below, 

/\  .  CHj.CHrCHs 

^        N  CH:CH.CHO 


O.CH, 


OH 

with  some  other  compounds.  It  is  obtained  by  distillation 
from  the  bark  of  the  cinnamon  tree,  and  is  a  yellow  oil, 
heavier  than  water,  and  is  used  in  flavoring,  for  perfumes, 
and  in  pharmacy. 

(c)  Oil  of  Cloves. — This  oil  is  practically  all  eugenol 
with  a  little  sesquiterpene.  It  is  obtained  from  the  dried, 
unopened  flower  buds  of  the  clove  tree,  growing  in  the  East 
and  West  Indies.  It  is  a  yellow  oil,  heavier  than  water,  and 
is  used  in  pharmacy,,  perfumery,  and  for  flavoring. 

(d)  Oil  of  Lemon. — This  is  mostly  a  terpene,  limonene, 
C10H16,  with  less  than  10  per  cent,  of  citral, 

CH,\ 

>C:CH.CHj.CH2.C:CH.CHO 
CH,/  I 

CH3 

to  which  the  odor  is  due,  and  many  other  compounds  such 
as  terpenes,  alcohols,  aldehydes,  and  esters.  It  is  obtained 
from  the  rind  of  lemons  either  by  rupturing  the  oil  cells  over 
a  sponge,  or  rolling  in  a  vessel  lined  with  spikes,  or  by  dis- 
tillation, or  expression.  The  two  latter  methods  do  not 
yield  as  good  an  oil  as  the  sponge  method.  It  is  a  pale 
yellow  oil,  lighter  than  water,  and  its  uses  are  the  same  as 
for  clove  and  cinnamon  oils. 


VOLATILE  OILS  AND  RESINS  51 

(e)  Oil  of  Mustard. — ^This  oil  is  chiefly  allyl  isothio- 
cyanate,  CH2:CH.CH2.N:C:S,  with  some  carbon  disulphide 
and  allyl  cyanide.  In  nature  it  occurs  in  the  seeds  of  black 
mustard  as  a  glucoside  of  potassium  acid  sulphate  and  allyl 
isothiocyanate,  called  potassium  myronate  which  is  hydro- 
lyzed  by  a  naturally  occurring  enzyme  when  water  is  present. 
The  seeds  are  first  expressed  for  the  fixed  oil,  then  treated 
with  water,  and  digested  in  the  cold  when  the  enzyme 
myrosin  converts  the  glucoside  into  glucose,  potassium 
acid  sulphate,  and  allyl  isothiocyanate.  The  latter  is  then 
distilled  off.  It  is  a  colorless  or  a  pale  yellow  oil,  heavier  than 
water,  with  pungent  odor  and  burning  taste.  It  is  used  in 
medicine  largely. 

(/)  Oil  of  Onion  consists  principally  of  allyl-propyl- 
disulphide, 

CHjiCH.CHj.S 

1 

CHj.CHj.CHj.S 

and  some  other  sulphides.  It  is  obtained  by  distillation 
from  onions.  It  is  not  of  much  value  commercially,  but 
is  the  compound  which  gives  to  onions  and  garlic  their 
characteristic  odor  and  taste. 

(g)  Oil  of  Peppermint  contains  a  great  number  of  differ- 
ent compounds  in  small  amounts — terpenes,  alcohols,  esters, 
acids,  and  aldehydes,  but  principally  menthol,  a  closed-chain 
compound  but  not  a  benzene  compound : 

CHj.CHj  CHs 

/  \  / 

CHj.CH  CH.CH 

\  /  \ 

CHj.CH  CHa 

I 
OH 

This  is  a  white,  crystalline  solid  at  ordinary  temperatures 
and  can  be  obtained  from  peppermint  oil  by  freezing.  It 
is  used  in  medicine.  The  peppermint  oil  itself  is  obtained  by 
steam  distillation  of  the  peppermint  plant  and  is  a  pale 
greenish-yellow  oil  which  darkens  on  standing.  It  is  lighter 
than  water  and  is  used  in  medicine  and  for  flavoring  to  a 
very  great  extent. 


52 


PLANT  COMPOUNDS 


(h)  Oil  of  Roses,  called  attar  or  otto  of  roses.  This  oil  is 
composed  of  geraniol,  CioHnOH,  and  citronellol,  C10H19OH, 
both  open-chain  or  aliphatic  alcohols.  There  are  also  some 
esters  and  paraffins  present.  It  is  obtained  by  distillation 
of  roses  which  are  grown  for  the  most  part  in  Bulgaria 
and  Roumania,  "the  rose  garden  of  the  world."  It  is  a 
pale  yellow  oil,  lighter  than  water,  with  a  very  delicate  odor. 
Attar  of  roses  is  very  high  priced  and  is  frequently  adul- 
terated with  geranium  oil  which  resembles  it  somewhat. 

(i)  Oil  of  Sassafras  consists  of  safrol, 

CH2.CH:CHj 


\       ./  ^NTHj 


and  a  number  of  terpenes,  etc.  It  is  obtained  by  distilling 
the  root  bark  of  the  sassafras  tree  which  is  very  common  in 
the  United  States.  It  is  usually  a  reddish-yellow  liquid, 
heavier  than  water,  and  is  used  for  scenting  cheap  soaps  and 
in  flavoring.  It  is  one  of  the  cheaper  oils. 
(j)  Oil  of  Thyme  is  chiefly  thymol, 


CHj 


\         /OH 

\/ 
Ca.CH.CHi 


and  carvacrol,  isomeric  phenols.  The  former  is  obtained 
from  thyme  oil,  and  is  used  as  an  antiseptic.  It  is  a  crystal- 
line solid.  The  other  constituents  of  thyme  oil  are  esters, 
hydrocarbons,  etc.  Thyme  oil  is  yellowish-red  when  impure, 
due  to  action  of  the  phenols  on  the  iron  stills;  and  light 
yellow  when  pure.    It  is  lighter  than  water;  used  in  medi- 


VOLATILE  OILS  AND  RESINS 


53 


cine,  and  as  a  cheap  perfume  for  soaps.  It  is  distilled  from 
the  leaves  and  flowers  of  an  herb  that  grows  largely  in  Spain 
and  France. 


Fig.   11.- 


-The  proper  way  to  collect  crude  turpentine.     Forest  Service, 
United  States  Department  of  Agriculture. 


{k)  Oil  of  Turpentine  is  a  terpene,  usually  pinene, 
C10H16,  with  some  other  isomers.  It  is  obtained  by  steam  dis- 
tillation of  the  resinous  exudate  of  the  long-leaf  pine  tree. 


54 


PLANT  COMPOUNDS 


This  sticky  liquid  which  flows  from  cuts  in  the  trees  is  com- 
posed of  a  resin,  colophony  (Section  29,  b),  and  an  essential 
oil  which  is  volatile  with  steam.  The  resin  is  left  in  the 
still.  The  turpentine,  which  is  lighter  than  water,  is  drawn 
off  and  sold  as  oil  or  spirits  of  turpentine.  Figs.  11  and  12 
illustrate  the  process  of  collection  and  distillation  of  tur- 
pentine. The  best  grades  come  from  this  country  and 
France.    Russia  produces  some  oil  of  poorer  quality.    It  is 


Fig.  12.- 


-Distilling  turpentine.     Forest  Service,  United  States 
Department  of  Agriculture. 


a  colorless,  mobile  liquid  with  a  faint,  pleasant,  ethereal 
odor  when  pure.  On  standing  there  is  formed  an  oxidized 
compound,  probably  an  aldehyde,  which  is  said  to  give 
turpentine  its  peculiar,  pungent  odor.  It  dissolves  sulphur, 
rubber,  phosphorus,  and  resins.  It  burns  with  a  very 
smoky  flame,  and  on  exposure  to  the  air  it  absorbs  oxygen, 
and  hardens,  much  like  the  drying  oils.  For  this  reason  it 
is  used  very  largely  in  making  paints  and  varnishes.  It  is 
also  employed  to  some  extent  in  medicine. 


VOLATILE  OILS  AND  RESINS  55 

(/)  Oil  of  Wintergreen  is  practically  all  methyl  salicylate, 

OH 

/\ 
/       \c00.CH3 


It  is  distilled  from  the  wintergreen  plant,  or  teaberry,  and 
from  the  bark  of  the  sweet  birch,  both  native  to  America. 
The  oil  is  yellow,  heavier  than  water,  and  has  a  very  pleasant 
taste  and  odor.  It  is  used  in  pharmacy  to  conceal  the  taste 
of  nauseous  drugs,  as  a  medicine,  and  for  flavoring.  Since 
methyl  salicylate  can  be  prepared  synthetically,  the  artificial 
product  is  largely  sold  in  place  of  the  true  oil. 

28.  Resins. — These  compounds  are  yellow  or  brown 
solid  substances,  more  or  less  transparent,  brittle,  and 
found  as  natural  or  induced  exudations  from  plants.  Some 
of  them  are  supposed  to  be  derived  by  oxidation  of  terpenes. 
Their  function  in  plants  may  be  to  serve  as  a  protective 
coating  for  wounds  and  cuts.  This  prevents  evaporation 
and  decay  iintil  new  cells  can  be  formed  to  permanently 
cover  the  wound.  As  resins  ooze  out  of  the  plant,  usually 
from  special  tubular  "resin  ducts,"  they  are  sticky,  thick 
liquids,  but  on  exposure  to  the  air  they  change  either  by 
oxidation  or  evaporation  of  some  natural  volatile  solvent, 
like  an  essential  oil.  Resins  are  insoluble  in  water,  soluble 
as  a  rule  in  alcohol  and  in  other  organic  solvents.  They 
decompose  on  heating  away  from  the  air,  and  burn  with  a 
smoky  flame.  Their  chemical  composition  is  very  complex, 
some  of  them  consisting  mostly  of  esters,  others  of  acids, 
and  still  others  of  uncertain  compounds  classed  under  the 
name  of  resenes.  In  addition  to  being  of  a  complex  nature 
when  purified,  they  frequently  occur  in  nature  as  an  exudate 
mixed  with  gums  and  called  Gum-resins,  which  emuhify 
with  water;  with  volatile  oils  called  Oleo-resins,  which  are 
softer  than  the  resins  proper;  and  with  volatile  oils  together 
with  benzoic  or  cinnamic  acid,  in  which  case  they  are  properly 
called  Balsams. 


56  PLANT  COMPOUNDS 

29.  Some  of  the  Common  Resins. — (a)  Amber  is  a  fossil 
resin  found  mostly  on  the  shore  of  the  Baltic  Sea,  frequently 
buried  in  the  earth.  It  is  the  hardest  resin  known,  varying 
in  color  from  yellow  to  black,  sometimes  clear  and  trans- 
parent, sometimes  cloudy.  Chemically  amber  consists  of 
acids  and  esters.  On  heating  in  a  retort  above  287°  C,  it 
melts  and  decomposes,  forming  water,  succinic  acid,  a  little 
volatile  fatty  acid,  oil  of  amber,  and  some  other  compounds. 
The  succinic  acid  and  oil  of  amber  are  used  in  pharmacy. 
Amber  is  used  mostly  for  ornamental  purposes,  although 
formerly  it  was  employed  in  the  manufacture  of  the  more 
expensive  varnishes. 

(b)  Colophony  or  Rosin  is  the  solid  residue  remaining 
after  oil  of  turpentine  (Section  27,  k)  has  been  distilled 
off.  It  occurs  naturally  as  an  exudate  with  turpentine 
from  certain  pine  trees.  It  is  a  brittle,  yellow  to  brown  solid, 
chemically  consisting  largely  of  an  acid.  It  unites  on  boiling 
with  sodium  or  potassium  hydroxide  to  form  a  deliquescent 
substance  called  resinate  used  in  making  soaps  and  for  sizing 
paper.  On  fusing  with  manganese  or  with  lead  oxides  it 
forms  resinates  soluble  in  linseed  oil  and  used  as  driers  in 
making  varnish.  On  dry  distillation  colophony  breaks 
up  into  hydrocarbons,  acids,  and  aldehydes.  Commercially 
two  products  are  obtained — rosin  spirit,  boiling  at  80°  to 
250°  C.  and  rosin  oil,  boiling  at  over  300°  C.  Rosin  spirit 
is  a  colorless  liquid  composed  of  hydrocarbons,  and  resem- 
bling oil  of  turpentine  for  which  it  is  used  as  a  substitute. 
Rosin  oil  is  a  heavy,  viscid  liquid,  colorless  to  brown,  com- 
posed mostly  of  high  boiling  point  hydrocarbons.  It  is  used 
in  making  rosin-grease  by  mixing  with  milk  of  lime,  for 
lubricating  axles,  and  for  making  printer's  ink.  Colophony 
or  rosin  itself  is  used  in  making  varnishes,  in  pharmacy, 
and  in  the  preparation  of  resinates,  rosin  spirit,  and  rosin  oil. 

(c)  Copal  is  a  name  applied  to  a  number  of  valuable 
resins.  Some  are  obtained  from  living  trees  in  Java,  Sumatra, 
and  the  Philippines.  Others  are  found  as  fossils  in  West 
Africa,  Madagascar,  and  East  Indies.  Copal  resins  may  be 
white,  yellow,  red,  brown,  or  brownish  black.  The  softer 
varieties  are  the  recent  resins  and  are  readily  soluble  in  the 


VOLATILE  OILS  AND  RESINS  57 

usual  solvents.  The  harder  kinds  are  the  fossil  resins  and 
are  practically  insoluble  in  the  usual  solvents  until  they 
have  been  melted  and  partly  decomposed,  when  they  dis- 
solve in  hot  turpentine  or  linseed  oil.  The  latter  copals 
are  the  more  valuable.  They  are  complex  in  composition, 
consisting  largely  of  acids  and  rescues.  They  are  used  in 
making  the  better  grades  of  varnish. 

(d)  Dragon's  Blood  is  found  in  Sumatra,  and  is  a  clear, 
deep  red  resin  composed  of  rescues  and  esters.  It  is  soluble 
in  alcohol  and  ether,  and  is  used  in  making  red  varnishes. 

(e)  Lac  or  Shellac  is  either  a  secretion  of  the  lac  insect 
or  produced  from  the  plant  sap  by  the  sting  of  this  insect 
on  the  twigs  of  certain  East  Indian  trees.  It  is  sold  in  sticks 
as  "stick  lac;"  melted,  purified,  and  poured  on  cold  surfaces 
to  cool  in  thin  plates  as  "shellac;"  or  poured  into  moulds  to 
form  "  button  lac."  It  is  pale  orange  or  red  when  pure,  much 
darker  when  impure.  The  red  shade  is  due  to  a  dye  secreted 
by  the  insect.  Bleached  shellac  is  made  by  passing  chlorine 
through  a  solution  of  lac  in  alkali.  This  precipitates  white 
lac  which  is  melted  and  pulled.  It  is  soluble  in  alcohol  and 
alkalies,  partly  soluble  in  ether.  Lac  is  composed  of  rescues 
and  acids.  It  is  used  extensively  in  varnishes,  for  stiffening 
hats,  as  a  constituent  of  sealing  wax,  etc. 

(/)  Mastic  and  Sandarac  are  similar  resins  found  in  Africa 
and  Australia,  occurring  in  the  form  of  "tears"  or  "solid 
drops"  of  rather  yellow,  translucent  material.  They  are 
partly  soluble  in  alcohol  and  turpentine,  completely  soluble 
in  ether.  They  are  composed  of  acids,  rescues,  and  bitter 
principles,  probably  alkaloids.  They  are  used  in  varnishes 
and  pharmacy,  in  the  latter  for  tooth  cements  and  plasters. 

30.  Some  of  the  Gum-resins,  (a)  Asafetida  is  found  on 
the  roots  of  certain  plants  in  Thibet  and  Turkestan  in  the 
form  of  tears  and  masses.  It  is  usually  yellowish  or  brownish 
in  color,  and  has  an  unpleasant  garlic  odor  and  bitter  char- 
acteristic taste.  Asafetida  is  composed  of  about  25  per  cent, 
of  gum  and  the  rest  resin  ester  with  a  little  volatile  oil  and 
some  other  compounds  in  small  amounts.  Its  use  is  restricted 
now  largely  to  veterinary  practice,  although  it  is  used  to 
some  extent  in  India  and  Persia  as  a  flavoring  agent  in  sauces. 


68  PLANT  COMPOUNDS 

(b)  Frankincense  or  Olibanum  is  found  on  certain  trees 
in  Arabia  and  Africa  as  yellow-brown  tears,  with  aromatic 
odor.  It  is  composed  of  resin,  gum,  some  volatile  oil,  and 
bitter  principle.  It  is  used  somewhat  in  pharmacy,  but 
more  generally  in  preparing  incense. 

(c)  Gamboge  is  found  on  trees  in  the  East  Indies  as  an 
orange-red  substance  which  is  soluble  in  alcohol.  It  is 
composed  of  an  ester,  an  acid,  and  a  gum.  It  is  used  in 
medicine  and  as  a  pigment. 

(d)  Myrrh  is  found  on  a  shrub  growing  in  Arabia  and  some 
other  eastern  countries.  It  occurs  in  reddish-brown  lumps 
of  oily  fracture,  fragrant  odor,  and  bitter  taste.  It  is  com- 
posed of  resin,  gum,  bitter  principle,  and  volatile  oil,  being 
used  in  medicine  and  in  making  incense. 

31.  Some  of  the  Oleo-resins  and  Balsams. — (a)  Benzoin 
is  a  balsam  and  comes  from  Sumatra  and  Siam,  that  from 
the  latter  place  being  of  the  better  quality.  It  occurs  in  tears 
or  masses  usually  reddish-brown  in  color,  having  a  very 
pleasant,  aromatic  odor,  and  is  soluble  in  alcohol.  Benzoin 
consists  of  a  volatile  oil,  benzoic  acid  esterified  with  a  resin 
alcohol,  and  some  other  compounds.  It  is  used  in  medicine 
as  an  antiseptic  and  in  perfumery. 

(6)  Canada  Balsam  is  incorrectly  named,  for  it  is  not  a 
true  balsam,  since  it  contains  no  benzoic  or  cinnamic  acid. 
It  is  an  exudate  from  the  balsam  fir,  and  is  a  thick  liquid, 
yellowish  in  color,  clear  and  transparent,  with  very  high 
refractive  index,  hardening  on  exposure  to  the  air.  It  is 
composed  of  a  volatile  oil  and  two  resins,  and  is  used  in 
medicine,  in  preparing  flexible  collodion,  and  in  mounting 
microscopic  specimens. 

(c)  Crude  Turpentine  is  the  thick,  viscous,  yellowish 
liquid  which  exudes  from  cuts  in  pine  trees,  usually  the  long 
leaf  pine,  in  the  United  States.  This  material  is  collected 
in  boxes  made  in  the  trees  or  better  in  cups  hung  on  the 
trees.  Fig.  11  shows  the  best  modern  method  for  collecting 
crude  turpentine.  The  first  year's  flow  called  "virgin  dip" 
is  the  best.  "Yellow  dip"  is  the  yield  -of  subsequent  years, 
and  "  scrape"  is  the  hardened  material  which  is  scraped  from 
the  trees.    This  last  is  the  poorest  of  all.    The  crude  tur- 


VOLATILE  OILS  AND  RESINS  59 

pentine  is  placed  in  copper  stills  and  distilled  with  steam  to 
separate  the  volatile  oil  of  turpentine  (Section  27,  k).  Colo- 
phony or  rosin  is  left  in  the  still  (Section  29,  6).  The 
oleo-resin  itself  has  no  value  except  as  a  source  of  oil  of 
turpentine  and  rosin.  Fig.  12  illustrates  the  distillation 
of  turpentine. 

(d)  ToLU  comes  from  South  America  as  a  nearly  solid 
mass,  yellow-brown  in  color,  of  aromatic  odor  and  taste.  It 
contains  both  benzoic  and  cinnamic  acids,  probably  united 
with  resin  alcohols,  and  in  addition  a  few  other  compounds. 
It  is  largely  used  in  medicine. 

32.  Compounds  Similar  to  the  Resins. — (a)  Rubber  or 
Caoutchouc. — Many  trees  contain  besides  the  so-called  sap 
and  other  liquids,  a  milky  juice  called  latex,  flowing  in 
special  elongated  cells  or  tubes.  The  function  of  this  latex 
may  be  to  carry  food  material  in  an  emulsified  form,  or  to 
serve  as  a  protection  when  the  tree  is  wounded.  It  oozes 
out  of  cut  surfaces,  hardens  on  exposure  to  the  air,  and 
serves  to  keep  out  water  and  bacteria  just  as  do  the 
resins  (Section  28).  This  latex  is  an  emulsion  of  fats.  Waxes, 
resinous  substances,  and  proteins  in  a  watery  fluid.  Certain 
trees,  more  particularly  in  South  America,  contain  in  the 
latex  minute  liquid  drops  of  a  hj'drocarbon,  having  the 
general  formula  of  a  terpene,  CioHie,  but  supposed  to  be  a 
chain  compound  and  not  a  ring  compound  like  a  terpene. 
These  drops  coagulate  on  exposure  to  the  air.  In  practice 
this  coagulation  is  hastened  by  the  smoke  of  burning  palm- 
nuts,  or  by  the  addition  of  salt  water,  wood-ash  lye,  or  alum. 
The  resulting  mass  forms  the  crude  rubber  of  commerce. 
To  obtain  the  latex  the  trees  are  cut  and  the  latex  gatheted 
much  as  is  maple  sap  in  the  United  States.  The  pure  hydro- 
carbon is  nearly  white  when  fresh  but  darkens  on  exposure 
to  the  air.  It  is  soluble  in  chloroform,  benzine,  and  toluene, 
and  is  rendered  hard  and  brittle  after  a  time  by  oils.  Chlorine, 
bromine,  and  strong  acids  destroy  it.  The  commercial 
material  is  practically  black  from  smoke  and  dirt,  containing 
in  addition  to  the  rubber  proper,  or  the  hydrocarbon,  some 
fat,  waxes,  and  proteins,  which  Vere  originally  in  the  latex. 
In  addition  there  are  chips,  bark,  and  dirt  of  various  kinds 
accidentally  present  or  intentionally  added. 


60  PLANT  COMPOUNDS 

The  crude  material  is  ground  and  washed,  and  for  use 
must  be  treated  with  sulphur,  metallic  sulphides,  or  metallic 
oxides.  The  pure  rubber  is  very  sticky,  but  on  heating  with 
5  to  10  per  cent,  of  sulphur  it  loses  its  stickiness,  becomes 
more  elastic,  and  is  the  usual  form  of  soft  rubber  from 
which  so  many  articles  are  manufactured.  When  heated 
with  antimony  pentasulphide  it  forms  "red"  or  "antimony" 
rubber.  Red  antimony  trisulphide  is  formed,  the  rest  of  the 
sulphur  uniting  with  the  rubber.  If  the  pure  rubber  is 
heated  with  25  to  30  per  cent,  of  sulphur,  it  forms  on  cooling 
a  hard,  hornlike  mass,  called  ebonite,  or  hard  rubber,  which 
finds  a  great  variety  of  uses  too  well  known  to  need  mention. 
The  sulphur  may  form  a  chemical  compound  with  the 
hydrocarbon  or  it  may  be  merely  a  physical  mixture  of 
sulphur  and  hydrocarbon. 

(6)  GuTTA  Percha. — ^This  material  is  somewhat  similar  to 
rubber,  occurring  in  the  latex  of  certain  East  Indian  trees. 
It  is  obtained  and  washed  like  crude  rubber  and  is  then  a 
fibrous  white  to  brown  mass,  tough  and  inelastic  when  cold, 
softening  greatly  on  heating.  It  is  soluble  in  carbon  disul- 
phide,  chloroform,  and  warm  benzine.  In  composition  it 
is  a  mixture  apparently  of  a  hydrocarbon,  CsHs,  and  two 
resins  which  are  oxygenated  bodies.  It  is  a  very  poor  con- 
ductor of  electricity  and  finds  its  principal  use  as  insulating 
material  for  wires,  etc. 

(c)  Chicle  is  also  a  product  of  the  coagulated  latex  of 
certain  South  American  trees,  and  is  used  in  the  United 
States  in  the  manufacture  of  chewing  gum.  It  is  composed 
of  a  true  gum  soluble  in  water,  resins,  the  hydrocarbon  of 
gutta  percha,  mineral  constituents,  and  some  other  com- 
pounds. The  purified  insoluble  portion  is  used  for  making 
chewing  gum. 

IV.     NITROGENOUS  COMPOUNDS 

33.  Nitrates  and  Ammonia. — There  is  always  present  in 
growing  plants  a  certain  amount  of  nitrates  that  has  been 
absorbed  by  the  plant  roots.  In  some  plants  the  amount 
may  be  1.5  to  3  per  cent,  of  the  dry  weight,  but  this  is  excep- 


NITROGENOUS  COMPOUNDS  61 

tional.  They  are  present  only  until  the  synthetic  processes 
are  able  to  convert  them  into  other  compounds.  This  is 
shown  by  the  fact  that  as  a  rule  most  of  the  nitrates  are  in 
the  root,  less  in  the  stem  and  leaves,  and  none  in  the  seed. 
Nitrates  are  present  only  as  they  are  absorbed  by  the  roots. 
Plants  do  not  form  nitrates  from  other  compounds  of  nitro- 
gen. Ammonia  is  sometimes  present  in  small  amounts  as  an 
absorbed  constituent,  for  some  plants  can  use  ammonium 
salts  as  well  as  nitrates  in  the  manufacture  of  proteins. 
Moreover,  it  may  occur  as  a  decomposition  product  of  pro- 
tein hydrolysis  (Section  49),  or  as  an  intermediate  product 
in  the  synthesis  of  proteins  (Section  69). 

34.  Amino-acids  and  Amides. — ^After  absorption  by  the 
plant,  nitrates  or  ammonia  are  changed  to  amino-acids  and 
amides.  Amino-acids,  sometimes  called  amido-acids,  are 
organic  acids  in  which  one  of  the  alkyl  hydrogen  atoms 
is  replaced  by  NH2.  A  common  one  is  amino-acetic  acid, 
CH2(XH2)COOH,  or  glycocoll.  The  amino-acids  as  a  group 
are  crystalline  substances  soluble  in  water.  They  will  unite 
with  acids  to  some  extent  on  account  of  their  amine  group 
and  with  bases  on  account  of  their  carboxyl  group.  Amides, 
sometimes  called  acid  amides,  are  organic  acids  in  which  the 
hydroxyl  of  the  carboxyl  group  is  replaced  by  XH2,  a  common 
amide  being  acet-amide,  CH3CONH2.  Acids  having  more 
than  one  carboxyl  group  may  have  one  or  all  of  the  hydroxyl 
groups  replaced  by  XH2.  They  are,  as  a  rule,  crystalline 
substances  and  more  or  less  soluble  in  water.  They  are 
basic  in  character,  forming  salts  with  acids. 

Apparently  the  formation  of  these  compounds  is  in  most 
cases  transitory;  they  are  merely  intermediate  products, 
existing  in  but  small  amounts  at  any  one  time.  There  are 
a  number  of  these  amides  and  amino-acids  found  in  plants, 
but  the  more  common  ones,  and  ones  which  illustrate  these 
compounds  very  well,  are  as  follows: 

(a)  AsPARAGiNE  is  fouud  in  considerable  quantities  in  pea 
and  bean  seedlings, 

CHj.CO.NHj 

I 

NHj.CH.COOH 

It  is  also  called  amino-succinamide. 


62  PLANT  COMPOUNDS 

(b)  Gltjtamine  occurs  to  a  large  extent  in  cucumber  and 
other  seedlings.    It  is  the  monamide  of  amino-glutaric  acid, 

CH2.CONH2 

I 

CH2 

I 

NH2.CH.COOH 

(c)  Argenine  occurs  largely  in  coniferse  or  trees  of  the 
pine  order,  and  possesses  a  more  complicated  structure  than 
the  others  mentioned, 


NH2 

NH:c/    * 

NH .  CH2 .  CH2 .  CH2 .  CH .  COOH 

I 
NH2 


(d)  Tyrosine  is  an  amino-acid  of  the  carbocyclic  series, 
found  in  many  plants, 

CH2.CH.c00H 


/       \  NH2 


OH 


35.  Proteins. — Proteins  are  compounds  containing  carbon, 
hydrogen,  oxygen,  and  nitrogen,  usually  sulphur,  and  some- 
times phosphorus.  They  are  the  most  complex  compounds 
known,  and  probably  the  most  important,  since  they  are  a 
necessary  constituent  of  every  living  cell,  whether  plant  or 
animal,  and  compose  most  of  the  dry  matter  of  animals 
except  the  bones.  Moreover,  plant  proteins  are  important 
not  only  to  plants  themselves,  but  also  to  animals,  since. the 
latter  are  dependent  for  the  most  part  on  the  ready-made 
proteins  of  plants  for  their  own  body  nitrogenous  compounds. 
The  name  itself  is  significant,  being  derived  from  a  Greek 
word  signifying  "preeminent." 

Chemically  proteins  are  combinations  of  alpha-amino- 
acids  or  their  derivatives.     Alpha-amino-acids  are  amino- 


NITROGENOUS  COMPOUNDS  63 

acids  in  which  the  amine  group  is  attached  to  the  carbon 
atom  next  to  the  carboxyl  group  (note  the  position  of  XH2 
in  the  formulas  given  in  Section  34).  The  composition  of 
proteins  is  about  as  follows:  Carbon,  .50  to  55  per  cent.; 
hydrogen,  0  to  7.3  per  cent.^;  oxygen,  19  to  24  per  cent.; 
nitrogen,  15  to  19  per  cent.;  sulphur,  0.3  to  2.5  per  cent. ;  and 
phosphorus,  if  present,  0.4  to  0.8  per  cent.  A  protein  molecule 
is  known  to  be  exceedingly  large,  the  molecular  weight  of 
different  proteins  being  estimated  at  from  4(KK)  to  1  (),()()()  in 
round  numbers.  A  formula  which  has  been  proposed  for 
zein — an  example  of  a  tjy^jical  plant  protein — will  give  some 
idea  of  the  complexity  of  the  molecule: 

Cj»oHm20«6N58S. 

Most  of  the  knowledge  of  proteins  is  based  on  studies 
of  the  animal  proteins.  Plant  proteins  in  general,  however, 
are  very  similar,  although  not  so  numerous. 

The  various  proteins  differ  somewhat  in  solubility,  some 
of  them  being  soluble  in  water,  others  in  dilute  alcohol, 
others  in  salt  solutions,  and  still  others  in  very  dilute  acids 
and  in  alkalies.  Strong  acids  and  alkalies  dissolve  proteins 
on  heating,  but  with  decomposition.  On  heating  with 
strong  sulphuric  acid  the  nitrogen  of  proteins  is  converted  to 
ammonium  sulphate,  from  which  ammonia  can  be  evolved 
with  sodium  hydroxide.  This  is  the  basis  of  the  quantita- 
tive estimation  of  proteins  (Section  92)  since  they  are  built 
up  from  a  series  of  amino-acids  or  their  derivatives  from  which 
ammonia  is  easily  split  off.  On  hydrolytic  decomposition 
they  generally  break  down  into  amino-acids. 

For  the  most  part  proteins  are  noncrystallizable,  belong- 
ing to  that  peculiar  class  of  compounds  called  colloids. 
Solutions  of  proteins  are  levorotary.  One  of  the  com- 
monest tests  for  a  protein  is  to  dissolve  it  in  concentrated 
nitric  acid  which  gives  a  yellow  color,  turning  to  orange  on 
the  addition  of  ammonium  hydroxide.  This  is  known  as 
the  xanthoproteic  reaction — or  "yellow  protein'  reaction. 
Chemists  are  familiar  with  the  fact  that  strong  nitric  acid 
stains  the  skin  yellow.  This  is  due  to  this  action  of  nitric 
acid  on  the  proteins  of  the  skin. 


64  PLANT  COMPOUNDS 

Some  of  the  proteins  in  solution  are  precipitated  unaltered 
by  saturating  the  solution  with  sodium  chloride,  ammonium 
sulphate,  or  magnesium  sulphate,  a  process  called  "salting 
out;"  others  are  thrown  down  in  a  changed  form  by  salts 
of  the  heavy  metals;  while  still  others  are  precipitated  as 
insoluble  salts  by  tannin.  No  single  reaction  is  common  to 
all  proteins.  According  to  their  properties  proteins  have 
been  classified  into  some  eighteen  groups  which  serve  to 
distinguish  them  and  aid  in  their  study. 

36.  Alkaloids. — These  are  plant  compounds  containing 
nitrogen  and  possessing  strongly  basic  properties.  They 
differ  from  the  other  organic  bases,  like  amines  and  amides, 
in  being  more  complex  in  structure  (the  exact  formula  is 
unknown  in  most  cases)  and  more  basic  in  reaction.  They 
differ  from  the  proteins  in  being  less  complex.  Their  most 
characteristic  property  is  their  very  powerful  physiological 
action  on  animals.  They  are  strong  medicines  or  strong 
poisons.  As  a  rule,  they  are  colorless  or  white,  crystalline 
solids,  and  contain  oxygen  in  addition  to  carbon,  hydrogen, 
and  nitrogen.  Nicotine  is  an  exception  being  a  liquid  and 
containing  no  oxygen.  Most  of  the  alkaloids  are  only  slightly 
soluble  in  alcohol.  They  dissolve  in  acids  with  the  formation 
of  salts.  From  their  solutions  they  are  as  a  rule  precipitated 
by  tannin,  phosphomolybdic  acid,  and  some  other  reagents. 
In  the  plant  they  occur  in  the  bark  of  the  stem  or  root,  in 
seeds,  and  in  the  fruit  rind.  Their  function  is  not  definitely 
known,  being  considered  by  some  authorities  as  end  products 
of  metabolism — waste  compounds  stored  where  they  are 
most  easily  removed;  other  authorities,  however,  claim  that 
alkaloids  are  intermediate  or  transitory  compounds  necessary 
for  the  growth  of  the  plant.  They  do  not  occur  in  all  plants, 
being  confined  for  the  most  part  to  the  poppy  and  legume 
families.  They  occur  as  salts  of  malic,  oxalic,  succinic,  tannic, 
or  some  other  plant  acid,  and  are  extracted  by  dissolving 
out  these  salts  with  appropriate  solvents,  and  separating 
the  alkaloid  from  the  acid.  Ordinarily  this  is  done  by  using 
a  mineral  acid  like  sulphuric  or  hydrochloric,  since  it  is  in 
this  form  that  the  alkaloids  are  used  commercially;  for 
example,  quinine  sulphate,  cocaine  hydrochloride,  etc. 


NITROGENOUS  COMPOUNDS 


65 


37.  Some  of  the  Common  Alkaloids. — (a)  Atropine, 
C17H23O3N,  is  a  white  crystalline  solid  with  a  bitter,  acrid 
taste  and  is  very  poisonous.  It  is  used  as  the  sulphate  for 
spasmodic  affections,  and  for  dilating  the  pupil  of  the  eye. 
Antidotes  are  emetics,  tannin,  or  charcoal. 


Fio.  13. — The  cultivated  variety  of  the  opium  poppy. 


(b)  Caffeine  or  Theine,  C8Hi(j02N4,  is  a  white,  silky  solid 
with  bitter  taste.  It  occurs  in  tea  and  coffee  in  combination 
with  a  complex  organic  acid,  the  compound  being  soluble  in 
water  and  is  hence  extracted  when  tea  and  coffee  are  treated 
with  water  for  beverages.  The  alkaloid,  occurring  to  the 
5 


66  PLANT  COMPOUNDS 

extent  of  1  per  cent,  in  coffee  and  2  per  cent,  in  tea,  exerts 
the  stimulating  effect  of  these  drinks.  In  addition,  however, 
there  are  also  extracted  tannin  (in  tea  only),  volatile  oil 
of  tea  or  of  coffee,  gum,  and  dextrin,  all  of  which  serve  to 
modify  the  effect  of  the  alkaloid.  Pure  caffeine  is  used  in 
medicine  as  a  stimulant,  and  to  cure  somnolence. 

(c)  Cocaine,  C17H21O4N,  is  a  colorless,  crystalline  solid 
with  bitter  taste,  and  producing  numbness.  Used  medicin- 
ally usually  as  the  hydrochloride,  C17H21O4N.HCI,  it  is  a  local 
anaesthetic.  It  is,  however,  a  dangerous  drug  to  use.  Anti- 
dotes are  morphine,  alcohol,  ammonia,  and  applications  of 
ice  to  the  head. 

(d)  Morphine,  C17H19O3N,  occurs  in  colorless,  shining 
crystals,  with  bitter  taste,  and  is  used  in  medicine  ordinarily 
as  the  sulphate,  (CnHi903N)2.H2S04.  It  is  the  chief  con- 
stituent of  opium  which  is  obtained  from  the  unripe  seed 
capsules  of  the  poppy  (Fig.  13).  Morphine  is  one  of  the 
most  valuable  narcotics  known,  but  it  is  a  very  dangerous 
drug  to  use  on  account  of  its  habit-forming  properties  and 
its  general  harmful  effect  on  the  mind  and  body  when  the 
habit  is  once  formed.  Antidotes  to  morphine  poisoning  are 
potassium  permanganate,  tannic  acid,  and  emetics. 

(e)  Nicotine,  C10H14N2,  is  a  colorless  liquid  turning  brown 
on  exposure  to  the  air,  with  acrid  taste.  It  is  one  of  the 
most  virulent  poisons  known.  In  small  doses  it  has  been 
used  in  medicine  as  a  sedative.  It  is  found  in  tobacco,  varying 
in  amounts  from  1  to  8  per  cent.  The  pleasant  as  well  as 
the  exceedingly  disagreeable  effects  of  smoking  and  chewing 
tobacco  are  probably  ascribable  to  nicotine.  In  the  impure 
form  it  is  used  as  an  insecticide. 

(/)  Quinine,  C20H24O2N2,  is  usually  a  white,  amorphous 
powder,  although  it  can  be  obtained  in  silky  needles,  and  has 
a  very  bitter  taste.  It  is  used  in  medicine  as  the  sulphate, 
(C2oH2402N2)2.H2S04,  bciug  particularly  efficacious  in  malaria, 
and  as  a  tonic  and  stimulant. 

(g)  Strychnine,  C21H22O2N2,  is  a  white  crystalline  powder, 
with  very  bitter  taste,  and  is  a  powerful  poison.  It  is  used 
in  medicine  in  very  small  doses  as  a  nerve  stimulant.  Anti- 
dotes are  potassium  permanganate,  emetics,  and  sedatives. 


ORGANIC  ACIDS  AND  THEIR  SALTS  67 

(h)  Theobromine,  C7H8O2N4,  is  a  white  crystalline  powder 
of  bitter  taste.  It  is  the  active  principle  of  chocolate  and 
cocoa,  occurring  to  the  extent  of  about  1  per  cent,  in  the 
cocoa  bean.  It  is  used  medicinally  to  some  extent,  its  effect 
being  similar  to  that  of  caffeine. 

V.    ORGANIC  ACIDS  AND  THEIK  SALTS 

38.  General. — In  discussing  the  various  plant  compounds, 
it  has  been  found  that  there  are  a  large  number  of  Organic 
acids  present  in  one  form  or  another.  The  fixed  oils  (Section 
14)  are  glyceryl  salts  of  various  fatty  acids  of  high  molecular 
weight;  some  of  the  volatile  oils  (Section  26)  are  esters  of 
organic  acids  both  of  the  chain  and  carbocyclic  series; 
some  of  the  resins  (Section  28)  are  composed  largely  of  very 
complex  acids  or  their  salts;  alkaloids  (Section  36)  exist  in 
combination  with  organic  acids  of  various  kinds.  But  in 
none  of  these  cases  do  the  acids  display  the  properties  which 
are  usually  ascribed  to  them,  namely,  that  of  a  sour  taste 
and  distinctly  acid  reaction.  There  are,  however,  in  many 
plants,  chiefly  in  the  fruits,  acids  which  respond  to  these 
tests.  As  mentioned  in  Section  67,  acids  may  be  in  part  at 
least  the  products  of  imperfect  oxidation,  or  intermolecular 
respiration.  They  may  be  in  part  waste  products  (compare 
oxalic  acid  below),  or  they  may  serve  some  definite,  physio- 
logical function. 

39.  Some  of  the  Common  Organic  Acids. — (a)  Citric  Acid 

CH2.COOH 
I 

HO.C.COOH 

I 
CH2.COOH 

is  found  in  the  free  state  in  lemons,  limes,  currants,  goose- 
berries, cranberries,  etc.  It  is  obtained  from  lemons  and 
limes  for  commercial  purposes,  and  is  used  in  medicine  and 
for  calico  printing.  It  forms  large  rhombic  crystals  with 
one  molecule  of  water  of  crystallization,  and  is  soluble  in 
water  and  in  alcohol.  On  boiling  with  lime  a  tricalcium 
salt  is  precipitated. 
(6)  Malic  Acid, 

ho.ch.cooh 
I 

CHs.COOH 


68  PLANT  COMPOUNDS 

occurs  free  in  unripe  apples,  grapes,  gooseberries,  and  in  many 
other  fruits;  as  the  acid  potassium  salt  in  some  cherries  and 
rhubarb;  and  as  the  acid  calcium  salt  in  mountain  ash 
berries.  It  is  prepared  from  the  latter,  and  used  to  some 
extent  in  medicine.  It  forms  deliquescent  crystals,  soluble 
in  alcohol.     The  normal  calcium  salt  is  insoluble  in  alcohol. 

(c)  Oxalic  Acid, 

COOH 

I 

COOH 

is  found  in  very  many  plants,  frequently  as  the  insoluble 
calcium  salt  in  the  form  of  crystals  (Fig.  17,  d).  It  occurs 
as  the  soluble  acid  calcium  salt  as  well  as  the  soluble  acid 
potassium  salt  in  sorrel  and  rhubarb.  It  forms  monoclinic, 
efflorescent  prisms  with  two  molecules  of  water  of  crystal- 
lization.    It  is  soluble  in  water  and  alcohol. 

(d)  Tartaric  Acid, 

HO.  CH.  COOH 

I 
HO.  CH.  COOH 

is  found  as  the  acid  potassium  salt  in  grapes;  and  as  the 
acid  potassium  and  acid  calcium  salts  in  pineapples.  When 
grapes  are  made  into  wine,  crude  acid  potassium  tartrate, 
called  "  argol,"  is  precipitated  in  the  vats.  When  purified  it  is 
called  "cream  of  tartar."  If  it  is  treated  with  sulphuric 
acid  and  recrystallized,  tartaric  acid  is  produced.  The  neutral 
calcium  salt  is  insoluble  in  water.  The  acid  potassium  salt 
is  soluble  in  water  but  practically  insoluble  in  alcohol. 
Tartaric  acid  crystallizes  in  large  monoclinic  prisms,  soluble 
in  water  and  in  alcohol.  The  sodium  potassium  tartrate  is 
Rochelle  salts,  and  potassium  antimonyl  tartrate  is  tartar 
emetic,  both  of  which  are  used  in  medicine. 

(e)  Tannic  Acid,  commonly  known  as  tannin,  is  extracted 
from  gall  nuts  (Section  40,  i),  and  forms  usually  a  light, 
yellowish-buff,  amorphous  powder  or  small  scales,  soluble  in 
water  and  in  alcohol,  insoluble  in  ether,  and  of  acid  reaction. 
It  has  an  astringent,  sour  taste,  precipitates  some  proteins, 


ORGANIC  ACIDS  AND  THEIR  SALTS 


69 


notably  gelatine  (Section  216),  and  forms  a  blue-black  pre- 
cipitate with  ferric  salts.    Its  formula  is : 

O  OH 

/^\ "       /^\ 

HO  /  >  C  —  O—  /  ^  OH 


HO 


HO 


COOH 


digallic  acid 


On  boiling  with  dilute  mineral  acids  it  hydrolyzes  to 
two  molecules  of  gallic  acid : 

COOH 


HO 


OH 


OH 


Tannic  acid  is  used  in  making  inks  with  ferric  salts  and  as 
an  astringent  in  medicine. 

40.  Tannins. — These  are  a  group  of  compounds  found  in 
various  plants,  and  in  all  parts  of  plants,  namely,  roots, 
bark,  stem,  leaves,  flowers,  and  fruit.  They  derive  their 
name  from  the  fact  that  they  will  tan  hides  to  make  leather. 
They  are  obtained  by  extracting  the  various  materials  with 
water  and  subsequent  purification.  The  extracts  contain  in 
addition  to  the  tannins  soluble  carbohydrates,  coloring  mat- 
ter, gums,  and  other  water  soluble  materials.  In  fact  their 
value  for  tanning  frequently  lies  partly  in  the  extractive 
material  other  than  the  tannins. 

Chemically  they  are  very  complex  and  not  well  known. 
Some  of  them  contain  digallic  acid  (Section  39,  e);  some 
contain  compounds  of  gallic  acid  with  dextrose,  as  glucosides ; 
while  others  contain  various  acids  derived  from  gallic  acid 
or  from  protocatechuic  acid, 

COOH 


0 

OH 


OH 


70 


PLANT  COMPOUNDS 


Their  properties  are  about  the  same  as  those  of  tannic 
acid.  The  property  of  precipitating  gelatine  makes  them 
valuable  for  tanning  hides,  and  that  of  precipitating  metallic 
salts,  for  dyeing.  Their  principal  use  is  in  tanning  hides, 
in  calico  printing,  dyeing,  and  making  inks. 

The  following  are  a  few  of  the  principal  kinds  of  tannin- 
containing  materials : 

(a)  Root  of  Canaigre,  a  beet-like  plant,  growing  in  south- 
western United  States,  and  Mexico.  It  contains  30  per 
cent,  of  tannin. 

(6)  Wood  of  Quebracho,  a  tree  from  South  America,  con- 
taining 24  per  cent,  of  tannin;  and  of  Catechu  or  Cutch, 
an  Indian  tree. 


Fig.  14. — Hemlock  hark  and  logs  to  be  used  for  tanning.     (Rhoads.) 

(c)  Wood  and  bark  of  Chestnut,  containing  8  to  12  per 
cent,  of  tannin,  and  of  Hemlock,  10  to  14  per  cent,  of  tannin. 
Fig.  14  shows  hemlock  bark  and  logs  being  collected  for 
tarming  purposes. 

(d)  Bark  of  Oak,  containing  5  to  15  per  cent,  of  tannin; 
and  of  Mangrove,  a  West  African  tree,  9  to  30  per  cent,  of 
tannin. 


EXERCISES  71 

(e)  Leaves  of  Sumach,  containing  15  to  30  per  cent,  of 
tannin;  and  of  Gambier,  an  Indian  shrub. 

(/)  Fruit  of  Divi-Divi,  a  West  Indian  tree,  containing 
30  to  50  per  cent,  of  tannin;  and  of  Myrobalans,  an  Indian 
and  Chinese  tree,  20  to  40  per  cent,  of  tannin. 

(g)  Acorn  cups,  called  Valonia,  of  a  certain  kind  of  oak,, 
containing  25  to  35  per  cent,  of  tannin. 

(h)  Dried  sap,  called  Kino,  from  Indian  and  African 
trees,  containing  75  per  cent,  of  tannin. 

(i)  Galls,  or  Nut  Galls,  a  diseased  excrescence  on  cer- 
tain Persian  and  Turkish  oak  trees,  caused  by  the  sting  of  an 
insect.  Galls  contain  60  to  75  per  cent,  of  tannin.  Tannic 
acid  is  the  purified  form  of  tannin  extracted  from  these  galls. 

EXERCISES 

1.  In  tabular  form  compare  two  monosaccharides,  two  disaccharides  and 
two  polysaccharides  as  follows:  Formula;  solubility;  action  with  Fehling's 
test;  whether  aldose  or  ketose;  action  with  iodine;  optical  activity;  products 
of  hydrolysis;  whether  storage  or  transport  form. 

2.  Given  a  mixture  of  dextrose,  levulose,  sucrose,  starch  and  cellulose 
in  solid  form,  how  can  the  presence  of  each  be  proved? 

3.  What  diffeience  if  any  exists  between  the  action  of  diastase  and  dilute 
hydrochloric  acid  on  starch? 

4.  Can  you  differentiate  corn  starch  from  potato  starch  physically  and 
chemically? 

5.  Differentiate  in  tabular  form  between  a  fixed  oil  and  a  volatile  oil  with 
respect  to  their  chemical  composition,  physical  properties,  functions  in  the 
plant  and  commercial  use. 

6.  How  many  points  of  similarity  can  be  found  in  the  hydrolysis  of  starch 
and  of  proteins?     Name  them. 

7.  Find  samples  of  the  statement:  "The  higher  the  molecular  weight 
in  a  series  of  compounds,  the  greater  the  insolubility." 

8.  How  can  the  presence  of  each  of  the  following  compounds  be  proved 
in  a  mixture  of  stearin,  zein,  cellulose,  benzaldehyde? 

9.  What  is  the  meaning  of  each  of  the  following  words  used  in  this  chapter: 
Physiologically,  empirical,  condensation,  hydrolytic,  decorticate,  alkyl, 
reduction,  transport  form,  storage  form,  hydrate,  fermentable,  amorphous, 
anhydride,  trihydric,  monobasic,  ester,  unsaturated,  carboxyl,  mineral  acid, 
aliphatic,  carbocyclic. 

(Forming  the  habit  of  using  a  dictionary  or  a  reference  book  as  soon 
as  a  word  is  used  whose  meaning  is  not  definitely  understood  is  imperative.) 

REFERENCES 
Allen.     Commercial  Organic  Analysis,  4th  ed.,  vols,  i,  ii,  iii,  iv,  v,  and  vi. 
Browne.     Handbook  of  Sugar  Analysis. 
Cross  and  Bevan.     Cellulose. 

Haas  and  Hill.     The  Chemistry  of  Plant  Products. 
Parry.     The  Chemistry  of  Essential  Oils. 

Rogers.  Manual  of  Industrial  Chemistry,  Chapters  24,  25,  28,  29,  31-37, 
43,  44,  47. 

Thorp.     Outlines  of  Industrial  Chemistry,  pp.  317-395,  521-532. 


CHAPTER    II 
GERMINATION  OF  THE  SEED 

The  seed  of  a  plant  contains  besides  the  growing  part  or 
embryo,  food  material  to  nourish  the  seedling  until  it  can  pro- 
duce enough  roots  and  leaves  to  be  independent.  The  food 
is  stored  away  in  a  very  concentrated  form  either  in  seed 
leaves  called  cotyledons,  which  are  part  of  the  embryo,  or 
in  a  special  depository  called  the  endosperm  which  is  merely 
connected  with  the  embryo.  Peas  and  beans  are  good  ex- 
amples of  seeds  with  food  in  cotyledons;  corn  and  wheat,  of 
those  with  food  in  endosperms.  The  food  material  in  the 
cotyledons  or  in  the  endosperm  consists  of  starch,  oil,  and 
protein,  the  relative  amounts  of  which  vary  with  the  kind 
of  seed.  Fig.  19  shows  the  interior  of  a  corn  kernel  and  the 
distribution  of  these  foods. 

41.  Conditions  for  Germination. — In  germinating,  a  seed  first 
sends  out  a  primary  root  which  starts  down  into  the  soil, 
then  it  puts  forth  toward  the  light  a  seed  bud  or  plumule, 
with  or  without  its  attendant  cotyledons  as  the  case  may  be. 
Only  under  certain  conditions,  however,  will  a  seed  germinate, 
and  these  conditions  are:  Presence  of  a  certain  amount  of 
water,  oxygen,  and  heat.  All  three  of  the  conditions  must  be 
fulfilled  or  no  growth  will  result.  If  seeds  are  kept  dry,  even 
though  they  may  be  in  a  warm  place  and  surrounded  by 
air  which  contains  all  the  oxygen  ever  needed  by  plants, 
they  will  not  sprout.  They  will,  however,  retain  their 
vitality  for  a  long  time,  several  years  being  the  ordinary 
maximum,  although  some  seeds  have  grown  after  being 
kept  fifty  or  one  hundred  years.  So  also,  if  seeds  are  placed 
in  water  freed  from  air,  and  kept  warm,  no  germination 
results,  because  the  water  prevents  oxygen  from  reaching 
the  seed.  Under  these  conditions,  however,  seeds  will  decay 
(72) 


WATER  73 

in  a  short  time,  because  of  the  influence  of  bacteria  which 
act  in  the  presence  of  moisture,  but  not  otherwise.  This 
indicates  the  importance  of  planting  seeds  in  aerated  soil, 
not  in  soil  saturated  with  water.  Seeds  under  the  latter 
condition  will  decay.  And  finally  if  seeds  are  supplied  with 
sufficient  moisture  and  are  well  aerated,  but  kept  cold,  no 
germination  will  occur.  It  is  absolutely  necessary  that  there 
be  present  sufficient  water,  oxygen,  and  heat. 

42.  Water. — ^The  food  material  packed  away  in  the 
cotyledons  or  endosperm  is  anhydrous  and  insoluble.  To 
be  transported  from  the  cells  in  which  it  is  stored  to  the 
growing  root  and  plumule  where  it  can  be  used  in  manufac- 
turing new  cells,  this  food  material  must  be  changed  to  a 
soluble  form.  The  chemical  change  which  makes  starch, 
oil,  and  protein  soluble-  is  hydrolytic  in  character;  that 
is,  water  is  necessary  to  break  down  the  insoluble  mole- 
cules of  stored  food  into  soluble  molecules  of  transportable 
food.  Certain  catalytic  agents  or  enzymes  are  necessary 
for  this  hydrolytic  action.  There  must  be  in  addition 
enough  water  to  dissolve  the  soluble  compounds,  and  to 
keep  the  new  cells  properly  distended  as  fast  as  they  are 
formed. 

A  seed  in  the  air  dry  condition  contains  about  10  per  cent, 
of  water,  but  to  start  germination  there  must  be  present 
about  30  per  cent.  The  water  is  imbibed  in  part  through 
the  seed  coat,  but  mostly  through  small  openings  where  the 
seed  was  attached  to  the  parent  plant  and  adjacent  to  the 
embryo.  This  absorption  or  imbibition  of  water  is  apparently 
caused  by  an  attraction  which  the  contents  of  the  seed  have 
for  water.  Starch,  for  example,  will  take  on  water  and  form  a 
weak  chemical  union  with  it,  something  like  water  of  crj'stal- 
lization.  Other  parts  of  the  seed  also  have  an  affinity  for 
water,  a  sort  of  molecular  attraction  for  it.  This  causes  the 
water  to  enter  the  seed. 

There  are  several  factors  which  affect  the  absorption  of 
water  by  the  seed.  Within  reasonable  limits  the  higher  the 
temperature  the  more  rapidly  water  is  absorbed.  This  is 
because  the  attraction  of  the  seed  contents  for  water  is 
increased  with  rising  temperature,  as  is  true  of  very  many 


74  GERMINATION  OF  THE  SEED 

chemical  reactions.  Another  factor  affecting  the  intake  of 
water  by  the  seed  is  the  amount  of  salts  dissolved  in  the 
water.  The  more  salts  in  solution,  the  less  water  is  absorbed, 
for  the  salts  have  a  counter-attraction  for  water  and  pre- 
vent its  entering  the  seed  so  readily.  Strong  salt  water 
or  too  much  soluble  fertilizer  around  seeds  will  prevent 
their  germination.  This  is  the  reason  why  seeds  do  not 
germinate  in  some  of  the  "alkali  soils"  of  the  west — there 
is  too  much  soluble  salt  in  the  soil  moisture.  Some  salts, 
of  course,  are  poisonous  to  seed  plants  and  so  cause  death, 
but  ordinarily  harmless  salts,  if  present  in  excessive  amounts, 
act  only  by  keeping  water  from  the  seed.  It  is  doubtful 
if  seeds  can  absorb  enough  water  from  saturated  air  to 
germinate,  hence  direct  contact  with  water  films  is  necessary; 
and  a  third  factor  in  the  amount  of  water  absorbed  by  seeds 
is  the  amount  of  seed  surface  in  contact  with  water.  The 
finer  the  soil  particles  in  the  seed  bed,  the  more  points  of 
contact  w^ith  the  seed,  and  since  each  soil  particle  is  sur- 
rounded by  a  water  film,  therefore  the  more  water  in  contact 
with  the  seed. 

.  43.  Oxygen. — In  forcing  the  roots  down  into  the  soil  as 
well  as  the  plumule  up  through  the  soil,  and  in  forming 
compounds  from  which  new  tissue  is  constructed,  the  ger- 
minating seed  requires  energy.  This  energy  is  derived  from 
the  oxidation  of  oils,  carbohydrates,  and  possibly  of  protein 
materials.  Just  as  in  a  steam  engine  where  oxidation  of 
coal  or  wood  results  in  various  forms  of  energy  such  as  heat 
and  work,  and  just  as  in  the  animal  where  oxidation  of  oils 
and  carbohydrates  results  in  various  forms  of  energy  such 
as  heat,  work,  and  formation  of  compounds,  so  in  the  germ- 
inating seedling  oxidation  of  material  results  in  the  various 
forms  of  energy  necessary  to  produce  a  plant.  This  oxida- 
tion, or  respiration  as  it  is  called,  requires  the  presence  of 
free  oxygen,  and  the  products  of  combustion  are  carbon 
dioxide  and  water  in  the  case  of  starch  and  sugars.  In  the 
case  of  oils,  probably  a  sugar  is  first  formed.  Both  oils  and 
carbohydrates  contain  carbon,  hydrogen,  and  oxygen,  but 
carbohydrates  contain  a  much  larger  proportion  of  oxygen 
than  do  oils.   It  is  highly  probable  that  intermediate  products 


HEAT  75 

are  formed  in  part  before  carbohydrates  are  completely 
converted  to  carbon  dioxide  and  water.  Germinating  seeds, 
then,  absorb  not  only  water,  but  oxygen,  and  give  off  or 
respire  carbon  dioxide  and  water.  The  water  formed  in 
respiration  remains  for  the  most  part  in  the  cells  where  it 
is  formed,  and  serves  as  solvent  water  or  chemical  water 
in  changing  insoluble  compounds  to  soluble  compounds. 
Temperature  is  a  very  important  factor  in  oxidation,  and 
within  limits  the  higher  the  temperature  the  faster  the 
oxidation. 

Unlike  ordinary  chemical  oxidation  or  combustion,  respira- 
tion in  seeds  is  not  a  direct  union  of  oxygen  with  another 
substance.  Variations  in  quantity  or  pressure  of  oxygen 
have  little  effect  on  the  rate  of  oxidation,  as  they  have  in  the 
case  of  true  combustion.  Moreover,  outside  of  the  seed, 
substances  like  starch  do  not  oxidize  except  at  high  tempera- 
tures, and  yet  in  the  seed  oxidation  goes  on  at  relatively  low 
temperatures.  Oxidation  in  the  seed  is  due  rather  to  the 
presence  of  certain  catalytic  agents,  or  enzymes,  which  act 
as  aids  in  making  oxygen  unite  with  seed  materials. 

Oxidation  in  the  seed  causes  loss  of  material,  as  might  be 
expected.  In  corn  grain,  for  example,  it  has  been  noted  that 
half  of  the  reserve  food  material  has  disappeared  in  three 
weeks,  due  to  oxidation.  Energy  produced  by  this  oxidation 
can  be  observed  in  the  movements  of  root  and  plumule, 
in  the  formation  of  new  compounds,  and  in  the  production 
of  heat.  A  mass  of  seeds  enclosed  in  a  non-conducting  vessel 
has  been  observed  to  raise  the  temperature  5°  to  10°  C. 
during  germination.  This  production  of  heat  in  the  germin- 
ating seed  is  of  value  in  stimulating  the  solution  of  food 
material  and,  in  general,  in  quickening  the  germination. 

44.  Heat. — It  has  been  noted  how  temperature  or  amount 
of  heat  affects  germination.  Seeds  can  germinate  over  a 
wide  range  of  temperature;  some  seeds,  wheat,  for  example, 
will  germinate  at  nearly  0°  C,  but  most  seeds  at  not  less 
than  5°  C.  The  upper  limit  of  germination  is  about  40°  C, 
although  cucumber  seeds  will  germinate  at  46°  C.  Each 
seed,  however,  has  an  optimum  temperature,  and  although 
this  varies  for  different  seeds,  it  is  not  far  from  30°  C.    Not 


76  GERMINATION  OF  THE  SEED 

all  of  the  necessary  heat  need  come  from  without;  vigorous 
respiration  of  the  germinating  seed  will  produce  some  of  the 
necessary  heat,  as  noted  in  the  preceding  section. 

45.  Food  for  the  Seedling. — ^The  insoluble  compounds 
which  supply  nourishment  to  the  growing  seedling,  and  which 
furnish  material  for  oxidation,  are  starch  (Section  8),  oil 
(Section  14),  and  proteins  (Section  35).  The  chemical 
changes  taking  place  in  these  compounds  are:  First,  the 
hydrol>i;ic  action  which  makes  them  soluble;  and  second, 
the  oxidation  reaction  which  changes  starch  and  oil  ulti- 
mately to  carbon  dioxide  and  water.  It  was  stated  in 
Sections  42  and  43  that  these  reactions  were  brought  about 
by  certain  catalytic  agents  called  enzymes. 

46.  Enzymes. — Enzymes  are  amorphous  substances  made 
by  living  cells,  but  which  can  act  independently  of  the 
living  cell.  They  are  not  organized  bodies,  that  is,  they 
have  no  life  in  themselves.  They  are  soluble  in  glycerine  and 
in  water,  insoluble  in  alcohol,  and  can  be  obtained  from 
living  tissue  by  pulverization,  extraction  with  glycerine  or 
water,  and  purified  by  alternate  precipitation  with  alcohol 
and  solution  in  water.  Chemically  they  are  protein-like 
in  character,  although  they  have  never  been  obtained  pure 
enough  to  have  their  constitution  accurately  determined. 
The  mode  of  action  is  catalytic,  that  is,  they  start  a  reaction 
or  change  its  rate.  In  most  cases  it  is  thought  that  a  given 
reaction  in  the  seed  will  go  on  by  itself,  but  so  slowly  as 
to  be  almost  imperceptible.  A  catalytic  agent  hastens  the 
reaction  so  that  the  changes  take  place  quickly.  The  catalytic 
agent  suffers  no  permanent  change  by  the  reaction,  and  a 
small  amount  of  catalyst  under  optimum  conditions  can  cause 
an  almost  indefinite  amount  of  chemical  change.  Catalytic 
agents  are  not  confined  to  enzj^mes.  An  example  of  an 
inorganic  catalyst  is  manganese  dioxide  in  the  generation  of 
oxygen  from  potassium  chlorate.  Manganese  dioxide  comes 
out  of  the  reaction  unchanged;  potassium  chlorate  is  reduced 
to  potassium  chloride.  The  manganese  dioxide  serves  to 
hasten  the  reaction  and  to  make  it  take  place  at  a  lower 
temperature  than  if  the  potassium  chlorate  were  decomposed 
alone.    Another  example  is  platinized  asbestos  in  the  contact 


AMYLASES 


77 


process  for  sulphuric  acid,  causing  sulphur  dioxide  and  oxygen 
to  unite  easily,  remaining  unchanged  itself. 

Enzymes  are  specific  in  their  activity.  There  are  numerous 
classes,  each  one  causing  or  hastening  a  particular  reaction, 
and  no  other.  The  principal  classes  that  are  effective  in 
changing  insoluble  stored  food  to  soluble,  movable  foods 
in  the  seed  are  amylases,  lipases,  and  proteases.  Enzymes 
which  cause  oxidation  are  called  oxidases. 


M 


% 


-^ 


Fig.  15. — Starch  grain  acted  upon  by  diastase,  showing  progressive 
solution.  Much  magnified.  Drawing  by  C.  A.  Smith  from  microscopic 
observation. 


47.  Amylases. — ^These  enzymes,  commonly  known  as 
starch  splitters,  are  the  best  known  of  the  seed  enzymes. 
Diastase  is  a  general  name  for  certain  members  of  this 
group  which  occur  in  plants.  In  the  presence  of  water  and 
suflBcient  heat,  and  from  the  energy  derived  by  oxidation, 
the  embryo  cells,  for  the  most  part,  produce  quantities 
of  these  diastatic  enzymes  which  pass  through  the  cell 
walls  into  the  starch  packed  cells  of  the  endosperm  or 
cotyledons.  There  they  cause  the  starch  to  unite  with  water 
and,  after  going  through  a  series  of  changes,  form  maltose  as 
^n  end  product,     In  some  cases,  although  not  so  often  in 


78  GERMINATION  OF   THE  SEED 

seeds,  dextrose  is  formed  from  maltose  by  another  enzyme. 
Apparently  there  is  a  different  kind  of  diastase  causing  each 
change.  Maltose  and  dextrose  are  soluble  and  diffusible. 
They  are  the  forms  in  which  carbohydrate  food  is  trans- 
ported to  the  growing  root  and  plumule  and  utilized  in  the 
formation  of  new  cells.  Fig.  15  shows  how  a  starch  grain  is 
gradually  broken  down  and  dissolved  away  by  the  action 
of  diastase  and  water. 

48.  Lipases. — There  is  not  much  known  of  these  enzymes, 
except  that  they  do  exist  and  have  the  property  of  splitting 
up  oil  by  hydrolysis.  There  are  produced  glycerine  and  the 
fatty  acid  or  acids  which  were  combined  with  the  glycerine 
to  form  the  oil.  Glycerine  is  soluble  and  diffusible.  The 
fatty  acids  are  insoluble,  but  probably  unite  with  such 
compounds  as  potash  within  the  cell  to  form  soap.  From 
glycerine  and  the  fatty  acids,  carbohydrates  are  formed 
in  the  growing  cells,  probably  by  oxidation. 

49.  Proteases. — These  enzymes,  called  also  protein  split- 
ters, have  the  power  of  hydrolyzing  protein  substances  and 
changing  them  to  simpler  bodies  such  as  albumoses,  peptones, 
amino-acids,  and  even  ammonia  compounds.  These  are  all 
soluble  and  diffusible.  After  transport  to  the  growing  points 
the  simpler  bodies  are  again  united  to  form  proteins. 

50.  Oxidases. — Respiration  or  oxidation,  not  being  a 
case  of  simple  combustion,  is  probably  due  to  the  activity 
of  these  enzymes  which  have  the  power  of  causing  oxygen 
to  unite  with  various  compounds.  Under  their  influence, 
starch  and  maltose  are  oxidized  to  carbon  dioxide  and  water; 
oils,  as  well  as  glycerine  and  fatty  acids,  are  oxidized  to 
carbohydrates  and  possibly  directly  to  carbon  dioxide  and 
water. 

EXERCISES 

1.  Is  hydrolysis  of  a  fat  sufficient  to  change  it  to  a  transport  form?  Why 
or  why  not? 

2.  Of  what  use  is  each  of  the  following  to  germination:  Hydrolysis, 
oxidation,  dextrose,  starch,  enzymes? 

3.  What  three  kinds  of  reactions  does  a  germinating  seed  use?  What  is 
the  purpose  of  each? 

4.  Is  it  usually  somewhat  warmer  next  to  a  germinating  seed  than  it  is 
at  a  little  distance  from  it?     If  so,  why? 


REFERENCES  79 

5.  What  is  the  meaning  of  the  following  words:  Embryo,  cotyledon, 
endosperm,  plumule,  anhydrous,  energy,  diffusible,  carlx)hydrate,  protein, 
maltose  and  chemical  energy? 

6.  What  two  substances  that  you  have  studied  undergo  hydrolysis  in 
steps?     Name  the  steps  in  each  case. 

7.  In  what  respect  is  the  burning  of  coal  in  a  furnace  similar  to  a  reaction 
necessary  for  the  germination  of  a  seed?  What  is  the  most  essential  product 
in  each  case?     Are  there  any  waste  products? 

8.  Which  requires  the  more  oxygen  for  its  complete  oxidation,  100  grams 
of  stearin  or  100  grams  of  starch,  and  how  much  more? 

9.  What  is  the  reaction  of  the  germinating  seed  upon  litmus  paper?  How 
is  the  compound  which  causes  this  reaction  produced? 

10.  Would  you  think  it  possible  to  have  too  much  soluble  plant  food 
around  a  germinating  seed?  Why  or  why  not?  Answer  the  same  questions 
for  water. 

REFERENCES 

Bergen  and  Davis.    Principles  of  Botany. 
Coulter,  Barnes,  and  Cowles.     Text-book  of  Botany,  vol.  i. 
Curtis.     Nature  and  Development  of  Plants. 
Czapek.     Chemical  Phenomena  in  Life. 
Duggar.     Plant  Physiology. 
Ganong.     The  Living  Plant. 

Jost.     Plant  Physiology,  translated  by  R.  J.  H.  Gibson. 
Pfeffer.     Physiology  of  Plants,  translated  by  A.  J.  Ewart.     2d  ed.,  vol.  i 
Strasburger,  Jost,  Schenk,  and  Karsten.     A  Text-book  of  Botany,  trans- 
lated by  W.  H.  Lang.     10th  English  ed. 


CHAPTER  III 

GROWTH  OF  THE  PLANT 

As  soon  as  the  plumule  rises  above  the  surface  of  the 
soil  it  turns  green,  leaves  rapidly  form,  and  the  young  plant 
begins  to  live  independently  of  the  food  laid  up  for  it  in  the 
seed  by  the  parent  plant.  It  now  obtains  all  the  material 
it  needs  for  the  manufacture  of  new  tissue  from  the  air 
through  the  leaves,  and  from  the  soil  through  the  roots. 

I.     PLANT  FOOD 

51.  Definition. — Plant  food  is  material  which  enables  a 
plant  to  build  new  tissue  and  may  still  further  be  defined  as 
substances  supplying  an  element  or  elements  by  means  of 
which  a  plant  can  carry  on  its  normal  functions  of  gro^\i;h 
and  reproduction.  Some  elements  thus  supplied  become  a 
constituent  part  of  the  cells.  Other  elements  merely  help 
in  this  formation  of  cellular  substance.  Plant  foods  may 
exist  in  forms  readily  taken  up  by  the  plant,  in  which  case 
they  are  called  available  foods,  or  in  forms  not  easily  taken 
up  by  plants,  in  which  case  they  are  called  unavailable  foods. 
The  latter  must  go  through  certain  changes  before  they 
become  available.  To  be  available  a  plant  food  must  be  in 
a  water  soluble  form.^ 

52.  Essential  Elements. — For  its  normal  development 
every  crop  plant  must  be  supplied  with  food  containing 
the  following  ten  chemical  elements:  Carbon,  hydrogen, 
oxygen,  phosphorus,  potassium,  nitrogen,  sulphur,  calcium, 
iron,  and  magnesium.  Most  plants  contain  in  addition 
silicon,  sodium,  and  chlorine.    These  latter  elements  have 

*  To  the  botanist  true  plant  food  is  material  elaborated  by  the  plant  and 
then  used  in  building  cellular  tissue.     It  is  not  material  supplied  from  the 
outside.    These  substances  might  be  called  plant  food  materials.    But  to  the 
agriculturist  the  definition  in  the  text  is  the  most  rational  and  satisfactory. 
(80) 


PLANT  FOOD 


81 


not  been  proved  essential,  although  in  many  cases  plants 
seem  to  do  better  with  them  than  without  them.  The  first 
ten,  however,  are  absolutely  essential  to  the  plant. 

53.  Composition  of  the  Plant. — About  three-fourths  of 
the  total  weight  of  a  green  plant  is  water.  The  remaining 
one-fourth  of  dry  matter  is  manufactured  by  the  plant  and 
is  made  up  largely  of  fundamental  organic  substance  con- 


DRY  MATTER 
25^ 


Fig. 


16. — Diagram  showing  the  distribution  of  water  and  dry  matter  in 
plants.     Drawing  by  E.  DeTurk. 


taining  only  carbon,  hydrogen,  and  oxygen.  There  is  further 
some  organic  substance  which  includes  part  of  the  nitrogen, 
sulphur,  and  phosphorus.  The  remainder  of  the  dry  matter, 
containing  potassium,  calcium,  magnesium,  iron,  and  some 
of  the  nitrogen,  sulphur,  and  phosphorus,  in  organic  and 
inorganic  form,  is  necessary  for  the  formation  of  funda- 
mental substance,  although  not  a  part  of  it. 

Fig.  16  gives  a  graphic  illustration  of  how  water  and  dry 
6 


82  GROWTH  OF  THE  PLANT 

matter  are  distributed  in  plants,  and  of  what  the  dry  matter 
is  ultimately  composed.  The  percentages  are  general 
averages  of  green  plants. 

54.  Form  in  which  the  Elements  are  Absorbed. — Carbon 
enters  the  plant  in  the  form  of  carbon  dioxide  through  the 
leaves.  Oxygen,  as  an  element,  enters  the  plant  for  the  most 
part  through  the  leaves,  but  also  through  the  roots  and 
stems.  This  is  the  only  one  of  the  essential  elements  which 
is  taken  up  by  the  plant  in  the  elemental  form.  As  such, 
however,  it  is  not  used  in  making  compounds,  but  in 
destroying  compounds  by  the  production  of  energy  through 
the  oxidation  of  plant  substance.  The  same  thing  has 
been  noted  in  the  case  of  the  germinating  seed.  For  manu- 
facturing plant  substance  oxygen  is  absorbed  in  combina- 
tion with  carbon  as  carbon  dioxide,  or  in  combination  with 
hydrogen  as  water,  the  latter  being  taken  up  through  the 
roots  from  the  soil.  Water  also  supplies  the  hydrogen 
necessary  for  plant  life. 

All  the  other  elements  enter  the  plant  from  the  soil  through 
the  roots.  Phosphorus,  nitrogen,  and  sulphur  are  absorbed 
as  phosphates,  nitrates,  and  sulphates  respectively  of  one  of 
the  basic  elements,  usually  calcium.  Potassium  commonly 
enters  the  plant  as  carbonate  or  bicarbonate,  but  also  as  a 
salt  of  one  of  the  acid  elements — that  is,  as  a  phosphate, 
nitrate,  or  sulphate.  Calcium  and  magnesium  are  absorbed 
as  bicarbonate,  phosphate,  nitrate,  and  sulphate;  and  iron 
as  hydrated  ferric  oxide. 

It  is  to  be  noted  that  these  compounds  are  all  in  a  highly 
oxidized  form.  Lower  oxidized  compounds  such  as  phos- 
phites, nitrites,  and  sulphites  are  not  plant  foods.  They 
are  rather  plant  poisons.  The  same  thing  is  true  of  other 
lower  oxidized  compounds.  Ammonia  may  serve  as  a  plant 
food  in  some  cases,  but  in  this  form  it  is  a  base  and  not  an 
acid.  It  is  generally  true,  however,  that  nitrates  are  the 
best  form  of  nitrogen  for  crop  plants,  and  usually  are  the 
only  form  which  can  be  utilized.  Gaseous  nitrogen  of  the 
air  for  legumes  is  a  special  case,  and  will  be  discussed  later 
(Section  125). 

All  of  the  plant  foods  must  be  inorganic  in  nature  and 


PLANT  FOOD  83 

must  dissolve  in  water  before  the  plant  can  absorb  them. 
It  is  not  necessary,  however,  that  they  be  very  soluble.  A 
weak  solution  is  even  better  for  a  plant  than  a  strong  one. 
In  the  case  of  iron,  for  example,  enough  of  the  hydrated 
ferric  oxide  dissolves  in  the  soil  moisture  to  nourish  plants, 
although  hydrated  ferric  oxide  is  usually  regarded  as  a 
comparatively  insoluble  compound. 

55.  How  Absorbed. — ^As  stated  above,  part  of  the  plant 
food  is  absorbed  through  the  leaves  from  the. air  and  part 
through  the  roots  from  the  soil.  Considering  first  the  ab- 
sorption from  the  soil,  it  is  to  be  noted  that  not  all  of  the 
roots  of  plants  spreading  through  the  soil  will  absorb  water 
and  plant  food.  Only  the  very  fine  root  hairs,  located  near 
the  growing  tips  and  extending  but  a  short  distance  back  of 
them,  act  as  absorbers  of  plant  food  matter.  The  remainder 
of  the  roots  is  covered  with  a  hard,  corky  layer  which  is 
impervious  to  water.  Since  the  growing  tip  keeps  pushing 
forward,  the  feeding  ground  is  constantly  changing. 

The  root  hairs  are  long,  slender,  single  cells.  The  walls 
are  very  thin,  composed  largely  of  cellulose,  and  are  easily 
pervious  to  liquids.  Lining  the  inside  of  these  cells  is  a 
layer  of  protoplasm  which  serves  as  a  regulator  for  the 
entrance  and  exit  of  water  and  soluble  material.  Under 
normal  conditions  of  growth,  water  passes  into  the  root 
hairs  together  with  the  dissolved  plant  food.  These  materials 
pass  from  cell  to  cell  until  they  reach  the  long  conducting 
tubes  on  the  interior  of  the  root  and  stem  called  tracheae. 
Here  the  stream  of  liquid  is  forced  up  to  the  leaves  and  other 
parts  of  the  plant.  The  passage  of  any  particular  plant  food 
from  cell  to  cell  is  always  from  the  region  of  greater  con- 
centration of  that  particular  food  to  the  region  of  less  con- 
centration. Water  passes  into  the  root  hairs  and  from  cell 
to  cell  regardless  of  the  concentration  of  any  one  plant  food, 
but  from  the  region  of  less  total  concentration  to  the  region 
of  greater  total  concentration. 

56.  Selective  Action  by  the  Roots. — The  protoplasmic 
lining  of  the  root  hairs,  as  well  as  of  other  cells,  exhibits 
a  certain  amount  of  selective  action,  permitting  the  entrance 
of  some  substances  and  keeping  out  others.    To  a  limited 


84  GROWTH  OF   THE  PLANT 

extent  this  means  that  as  the  plant  needs  this  or  that 
plant  food  the  root  hairs  absorb  it.  For  example,  at  any 
one  time  nitrates  may  pass  in  freely  and  phosphates  may 
not.  Later  this  proceeding  may  be  reversed;  or  both  may 
enter.  On  the  other  hand  this  selective  action  does  not  seem 
very  perfect,  for  most  soluble  inorganic  compounds  will 
enter  a  plant"  even  when  very  harmful.  Still  further,  the 
protoplasmic  layer  may  exert  a  sort  of  decomposing  action 
on  a  salt  like  sodium  nitrate,  absorbing  the  nitrate  radical 
and  leaving  behind  the  sodium,  combined  probablj^  as  a 
carbonate.  Or  potassium  sulphate  may  be  split  up,  the 
potassium  being  absorbed  in  some  other  form,  possibly  as 
the  carbonate,  and  the  sulphate  left  behind,  probably  as 
sulphuric  acid.  Moreover,  it  prevents  such  cell  contents  as 
sugar  and  soluble  proteins  from  passing  out.  In  general, 
soluble  organic  compounds  do  not  pass  through  the  root 
hair  wall  or  protoplasm  in  either  direction.  In  other  words, 
crop  plants  can  not  absorb  organic  compounds  of  the  essential 
elements,  and  organic  compounds  such  as  acids  are  not 
excreted  by  the  plant  root  hairs.  The  acid  action  of  root 
hairs  is  due  to  the  excretion  of  carbon  dioxide  which  in  water 
forms  carbonic  acid,  capable  of  dissolving  certain  substances. 
This  excretion  of  carbon  dioxide  is  the  result  of  respiration 
or  oxidation  of  material  within  the  root  cells. 

57.  Withdrawal  of  Water  from  the  Roots. — Under  abnormal 
conditions,  such  as  when  the  soil  moisture  becomes  too 
concentrated  in  plant  food,  water  passes  out  of  the  root 
hairs  instead  of  into  them.  This  movement  of  water  extends 
back  from  cell  to  cell  and  results,  if  not  remedied,  in  the 
ultimate  death  of  the  plant.  Too  much  fertilizer  around  the 
roots  of  plants;  strong  brine  solution,  as  when  the  ice-cream 
freezer  is  emptied  on  the  grass;  white  alkali  in  the  west; 
all  these  are  familiar  causes  of  this  effect  of  withdrawing 
water  from  a  plant,  resulting  in  its  death.  This  outflow  of 
water,  however,  does  not  prevent  the  dissolved  salts  from 
entering  the  plant  at  the  same  time.  In  some  instances  the 
salts  themselves,  passing  into  the  plant  in  excessive  quanti- 
ties, stop  the  vital  activity  of  the  cells.  The  so-called  black 
alkali — or  sodium  carbonate — of  the  west  is  one  of  these 
poisonous  salts,  unless  in  very  dilute  solution. 


UTILIZATION  OF  PLANT  FOOD  85 

58.  Function  of  Roots. — Roots  serve  not  only  as  an  anchor- 
age for  the  plant,  to  hold  it  upright  and  prevent  its  being 
blown  down  or  knocked  over  easily,  but  also  as  ports  of 
entry  for  water  and  plant  food  through  the  root  hairs,  and  as 
"aqueducts"  or  water  carriers  for  the  rest  of  their  course. 
The  corky  layer  on  the  greater  part  of  the  roots  prevents 
loss  of  water  and  plant  food  on  their  way  up  into  the  plant. 


n.    UTILIZATION  OF  PLANT  FOOD 

59.  Use  of  Inorganic  Material. — Unlike  animals,  plants 
manufacture  carbonaceous  or  organic  matter  from  inorganic 
raw  materials.  All  that  the  plant  absorbs  are  inorganic 
compounds  dissolved  in  water.  From  these  it  makes  its  cells 
and  their  contents,  which  latter  are  very  complex  and  of  many 
different  kinds.  The  basis  of  all  the  organic  compounds  in 
plants  is  composed  of  carbon,  hydrogen,  and  oxygen,  and  is 
manufactured  in  the  leaves  for  the  most  part.  Energy  for 
this  chemical  synthesis  is  derived  from  the  sun's  rays.  That 
is,  the  energy  of  light  waves  is  transformed  into  potential 
energy  in  the  form  of  chemical  compounds.  Only  a  few  of 
the  light  waves  are  useful  in  this  work  and  of  the  sun's  total 
energy  only  1  to  2  per  cent,  is  utilized. 

60.  The  Spectrum. — The  sun's  rays  are  composed  of 
many  kinds  of  light  waves,  some  short  and  some  long,  some 
visible  and  some  not.  Those  that  are  visible  can  be  separated 
by  a  prism  into  a  so-called  spectrum  which  shows  the  colors 
of  the  different  waves  from  violet  to  red.  The  red  waves 
are  almost  twice  as  long  as  the  violet  waves.  It  is  the 
waves  near  the  red  part  of  the  spectrum  that  are  absorbed 
and  changed  to  potential  energy. 

61.  Chlorophyl. — ^To  absorb  these  light  waves  the  plant 
must  have  chlorophyl,  which  is  a  green  substance  manufac- 
tured by  the  plant  as  soon  as  the  plumule  emerges  into  the 
light.  It  is  composed  of  two  pigments,  blue  and  yellow,  if 
not  more.  One  of  these  pigments  at  least  contains  nitrogen 
and  phosphorus.  They  may  be  separated  by  appropriate 
means,    but    their   chemistry    is    little    understood.     This 


86 


GROWTH  OF  THE  PLANT 


chlorophyl  is  located  in  small  bodies  called  chloroplasts, 
principally  within  the  cells  of  the  leaves  (see  Fig.  18,  c). 
Leaves  are  particularly  well  adapted  to  their  purpose  of 
absorbing  light  waves,  being  broad  and  flat,  thus  exposing 
a  large  surface  to  the  light.  Moreover,  they  are  so  distrib- 
uted that  light  can  fall  on  them  to  the  best  advantage; 
as  can  be  seen  by  examining  the  grouping  of  leaves  on 
plants — a  grapevine  for  example. 


'D  OCD  CTDCDCDCZ^ 


Fig.  17 


Fig.  18 


Figs.  17  and  18. — Section  of  a  leaf.     Much  magnified. 

Fig.  17. — Across  the  whole  leaf,  a,  epidermis;  b,  palisade  cells  showing 
chloroplasts,  c;  d,  crystals  of  calcium  oxalate;  e,  spongy  parenchyma  also 
showing  chloroplasts,  c;  f,  air  spaces;  g,  stoma. 

Fig.  18. — Single  cell,  c,  chloroplasts;  s,  starch  grains;  n,  nucleus;  p, 
protoplasm.    Drawing  by  C.  A.  Smith. 


Chlorophyl  itself  does  not  develop  in  the  dark.  Potato 
sprouts,  for  example,  that  grow  in  a  dark  cellar  may  be  of 
considerable  size  and  small  leaves  may  develop,  but  they  are 


UTILIZATION  OF  PLANT  FOOD  87 

white  or  yellowish  in  color.  Grass  leaves  that  have  grown 
under  a  board  or  stone  are  lacking  in  chlorophyl. 

62.  Manufacture  of  Carbohydrate. — The  raw  materials, 
combining  to  form  the  chemical  compounds  which  store 
this  energy,  are  carbon  dioxide  and  water.  The  water,  as 
has  been  noted,  comes  up  from  the  soil  through  the  roots 
and  stems.  The  carbon  dioxide  enters  the  leaves  through 
small  openings  on  the  under  side,  called  stomata  (Fig.  17,  ^f). 
This  gas  passes  into  the  air  spaces  (Fig.  17,  /)  between  the 
cells  and  finally  through  the  cell  wall,  dissolving  in  the  cell 
sap  to  form  carbonic  acid.  Under  the  action  of  the  light 
waves  absorbed  by  the  chlorophyl,  carbonic  acid  probably 
breaks  up  into  formaldehyde  and  oxygen  according  to  this 
equation : 

H2CO3  =  CH2O  +  O2. 

The  oxygen  is  given  off  through  the  cell  walls  into  the  air 
spaces  and  out  through  the  stomata.  The  formaldehyde, 
dissolved  in  water,  of  course,  is  almost  instantly  condensed 
to  dextrose,  thus: 

6CH2O  =  CeHuOe. 

The  dextrose  is  acted  upon  by  an  enzyme  which  subtracts 
water  from  it  and  forms  starch  (Fig.  18,  s),  thus: 

n  C8H12O6  —  n  H2O  =  (CeHioOs)  n. 

Starch  is  usually  the  first  visible  compound  formed  in  this 
process  of  photosynthesis,  as  the  process  of  chemical  synthesis 
by  means  of  light  is  called.  In  some  cases,  however,  the 
dextrose  is  changed  to  sucrose.  This  process  of  starch  manu- 
facture goes  on  during  the  day  only.  No  synthesis  takes 
place  in  the  dark. 

63.  Transfer  of  Carbohydrates. — Starch  in  the  leaf  is 
only  the  temporary  form  of  manufactured  material.  During 
the  day  carbonaceous  matter  is  synthesized  more  rapidly 
than  it  can  be  removed,  and  the  cells  would  be  clogged  with 
soluble  food  if  it  were  not  changed  to  an  insoluble,  concen- 
trated form  for  temporary  storage.    At  night  when  no  car- 


88  GROWTH  OF  THE  PLANT 

bonaceous  matter  is  being  formed,  the  starch  is  acted  upon 
by  amylases  and  is  changed  probably  to  dextrose.  It  is 
thus  passed  from  cell  to  cell  by  diffusion  through  the 
cell  walls  and  plasmatic  linings  until  it  passes  out  of  the  leaf 
into  the  main  conducting  channels  of  the  plant.  These 
channels  are  the  so-called  sieve  tubes  located  outside  of  the 
tracheae,  or  passages  for  the  upward  current  of  water  and 
plant  food. 

Dextrose  moves  to  that  part  of  the  plant  needing  new 
material,  such  as  newly  expanding  leaves,  growing  tips, 
flowers,  or  roots.  At  these  points  other  changes  take  place 
in  the  dextrose.  It  may  be  reconverted  into  starch  for 
storage,  or  into  cellulose  for  cell  walls,  or  into  oils,  or  into 
any  other  of  the  numerous  plant  compounds. 

64.  Amount  of  Carbohydrate  Synthesized. — ^Averaging  the 
results  of  several  experiments,  it  can  be  said  that  during 
daylight  on  a  bright  day  one  square  meter  of  leaf  surface 
manufactures  about  one  gram  of  carbohydrate  material  in 
one  hour.  For  an  acre  of  corn  about  the  time  of  tasseling, 
there  is  manufactured  about  170  pounds  of  carbohydrate 
in  one  day. 

65.  Respiration. — As  has  been  shown,  the  manufacture 
of  carbohydrates  is  brought  about  by  the  energy  of  light 
waves,  and  the  process  is  called  photosynthesis.  The  manu- 
facture of  all  other  products  is  brought  about  by  the  energy 
released  on  the  oxidation  of  plant  material,  and  the  process 
is  called  chemosynthesis.  Oxidation  or  respiration  is  common 
to  the  growing  plant  just  as  it  is  to  the  germinating  seed, 
although  not  to  so  great  an  extent.  It  is  dependent  on  the 
activity  of  oxidases  in  the  presence  of  oxygen.  This  results 
in  the  production  of  carbon  dioxide  and  water,  and  a  con- 
sequent loss  of  plant  substance.  In  other  words  the  leaves 
of  plants  are  not  only  taking  in  carbon  dioxide  through  their 
stomata,  making  carbohydrates  with  water  and  giving  off 
oxygen,  but  they  are  also  absorbing  oxygen,  oxidizing  car- 
bohydrates, producing  water,  and  giving  off  carbon  dioxide. 
The  gain  of  plant  substance  through  photosynthesis, 
however,  is  much  greater  than  the  loss  through  respiration, 
for  it  is  obvious  that  a  growing  plant  gains  in  weight  of  dry 


UTILIZATION  OF  PLANT  FOOD  89 

matter.  It  does  not  lose  weight.  Experiments  have  shown 
that  the  material  assimilated  may  amount  to  thirty  times 
that  lost  by  respiration. 

66.  Products  of  Respiration. — ^The  gases  of  respiration, 
oxygen  and  carbon  dioxide,  can  pass  from  cell  to  cell  by 
diffusion,  being  dissolved  in  water  and  transported  like  other 
soluble  compounds.  The  greater  part  of  these  gases,  however, 
exists  in  the  intercellular  spaces  which  have  access  to  the 
outer  air  through  the  stomata  on  the  leaves,  and  the  lenticels 
in  the  bark  and  roots.  The  oxidation  of  material  liberates 
in  the  plant  several  forms  of  energy.  First,  heat  is  generated 
to  a  noticeable  extent  in  germinating  seeds,  flowers,  and 
buds,  though  for  the  most  part  it  is  dissipated  by  radiation, 
plants  having  a  much  larger  radiating  surface  in  proportion 
to  their  mass  than  do  animals.  Second,  work  results,  such 
as  movements  of  various  organs;  of  the  entire  plant;  or 
of  protoplasm  within  the  cells.  Food  is  also  transported. 
Third,  chemical  changes  are  brought  about,  such  as  the 
formation  of  new  compounds,  the  solution  of  some,  and  the 
precipitation  of  others. 

67.  Intermolecular  Respiration. — In  addition  to  ordinary 
respiration  which  takes  place  only  in  the  presence  of  free 
oxygen,  there  occurs,  especially  under  conditions  where 
oxygen  is  wanting,  a  process  of  oxidation  at  the  expense  of 
other  molecules  by  their  reduction.  That  is,  energy  for 
certain  processes  may  be  derived  by  a  reaction  between 
molecules  in  the  same  cell,  resulting  in  the  temporary 
release  of  oxygen  from  one  of  them.  This  may  be  called 
intermolecular  respiration.  The  products  of  such  oxidation 
are,  besides  carbon  dioxide  and  water,  ethyl  alcohol,  higher 
alcohols,  acids,  aromatic  compounds,  and  even  hydrogen. 
This  sort  of  oxidation,  it  must  be  remembered,  means  as 
much  reduction  as  oxidation.  Where  one  molecule  gains 
an  atom  of  oxygen  another  molecule  loses  it.  Plant  cells, 
however,  cannot  live  for  any  length  of  time  by  means  of 
intermolecular  respiration  alone.  All  crop  plants  must 
have  free  oxygen  for  their  development. 

68.  Manufacture  of  Oil. — Particles  or  films  of  oil  seem 
to  be  a  necessary  constituent  of  plant  cells  and  this  material 


90  GROWTH  OF  THE  PLANT 

is  made  from  carbohydrates — probably  dextrose.  Since 
oils  contain  less  oxygen  than  dextrose  or  other  carbohydrates, 
the  process  must  be  one  of  reduction — possibly  a  result  of 
intermolecular  respiration. 

69.  Manufacture  of  Protein. — By  far  the  most  important 
chemical  work  done  by  the  plant  is  the  making  of  proteins, 
the  most  complex  compounds  known.  Just  how  these 
compounds  are  manufactured  from  raw  materials  is  not 
thoroughly  understood.  Starting  with  carbohydrates — 
probably  dextrose — nitrates,  sulphates,  and  sometimes 
phosphates,  the  cells  of  plants  build  up  a  compound  which 
in  no  way  resembles  its  constituents.  The  nitrogen  and 
sulphur  are  no  longer  in  the  oxidized  condition,  in  fact, 
just  the  reverse.  In  other  words,  the  nitrates  and  sulphates 
are  reduced,  possibly  to  ammonia  and  free  sulphur.  Then 
they  are  combined  with  carbon,  hydrogen,  and  oxygen  from 
carbohydrates  to  gradually  build  up  the  complex  protein. 
One  of  the  first  nitrogen  compounds  to  be  formed  seems  to 
be  an  amino-acid.  It  has  been  suggested  that  nitrates  and 
sulphates  are  reduced  by  carbohydrates,  as  a  result  of 
intermolecular  respiration,  whereby  the  carbohydrates  are 
oxidized  in  part  to  oxalic  acid.  This  acid  unites  with  the 
bases  of  the  reduced  nitrates  or  sulphates,  namely,  calcium, 
potassium,  or  sodium.  Later  the  soluble  oxalates  of  potas- 
sium and  sodium  are  changed  to  insoluble  calcium  oxalate 
(Fig.  27,  d).  This  excess  of  calcium  may  possibly  be  furnished 
by  calcium  phosphate,  since  the  phosphoric  acid  radical  is 
used  in  making  some  proteins.  The  remainder  of  the  oxi- 
dized carbohydrates,  in  the  form  of  some  other  acids,  may 
unite  with  the  ammonia  to  form  amino-acids.  A  number 
of  these  amino-acids  uniting  together  with  sulphur  and 
sometimes  phosphorus  gradually  construct  a  protein. 

Proteins  are  made  to  a  great  extent  in  leaves,  but  their 
formation  is  not  restricted  to  the  leaves.  Other  parts  of  the 
plant  make  these  compounds  from  the  raw  materials.  Light 
is  not  directly  essential  for  their  formation.  The  necessary 
energy  is  derived  from  oxidation  of  carbohydrates  and  is  a 
chemosynthesis  as  in  the  case  of  oils.  The  presence  of 
carbohydrates  is,  of  course,  required  since  they  are  the  source 


UTILIZATION  OF  PLANT  FOOD  91 

of  carbon  for  the  proteins,  and  inasmuch  as  formation  of 
carbohydrates  depends  on  light,  protein  synthesis  takes 
place  usually  more  rapidly  in  the  light. 

70.  Transfer  of  Oil  and  Protein. — Just  as  starch  is  rendered 
soluble  and  transported  throughout  the  plant  to  parts  needing 
new  material,  so  are  oils  and  proteins  changed.  Lipases  and 
proteases  are  not  confined  to  the  seeds.  They  exist  anywhere 
in  the  plant  that  oil  and  protein  splitting  is  essential.  Oils 
are  hydrolyzed  to  glycerine  and  fatty  acids,  the  latter  to 
soap  just  as  in  the  seed.  Proteins  are  hydrolyzed  to  simpler 
compounds  such  as  albumoses,  peptones,  amides,  etc.  It 
is  not  known  whether  the  breaking  down  of  proteins  goes 
through  the  same  changes  in  reverse  order  as  the  synthesis, 
but  possibly  it  does.  The  course  of  dissolved  oils  and  pro- 
teins through  the  plant  is  the  same  as  that  of  dextrose,  or 
dissolved  carbohydrates. 

71.  Functions  of  Carbohydrate,  Oil,  and  Protein. — For 
respiration  and  the  consequent  production  of  energy  in  the 
plant,  carbohydrates  are  principally  used.  Oils  and  proteins, 
however,  may  serve  this  purpose.  For  the  manufacture 
of  cell  walls,  carbohydrates  are  employed.  As  was  seen  in 
Section  63,  soluble  material  like  dextrose  is  changed  to 
cellulose.  For  the  manufacture  of  protoplasm,  and  as 
storage  material  for  the  crop  of  the  following  year,  all  three 
kinds  of  material  are  important. 

72.  Protoplasm. — This  is  the  material  which  plays  the 
most  active  role  in  all  of  these  chemical  changes,  and  which 
must  be  constantly  renewed  in  old  cells  and  increased  for 
new  cells  (Fig.  18,  y).  Its  appearance  is  not  the  same  in 
different  cells  but  in  general  it  is  a  more  or  less  soft,  spongy, 
slimy,  granular  mass,  practically  colorless,  and  suspended 
in  water.  Embedded  in  it  are  always  the  nucleus  or  real 
seat  of  life,  and  varying  with  conditions,  chloroplasts 
or  chlorophyl  cells,  particles  of  starch,  droplets  of  oil,  and 
many  other  substances  of  more  or  less  temporary  nature. 
The  approximate  chemical  composition  of  the  dry  matter 
of  protoplasm  is  as  follows : 

50  to  66  per  cent,  proteins. 

25  to  17  per  cent,  oils  and  carbohydrates. 


92  GROWTH  OF  THE  PLANT 

25  to  17  per  cent,  organic  acids,  particularly  amino-acids, 
organic  bases,  and  mineral  salts  of  potassium,  magnesium, 
calcium,  and  iron. 

73.  Seeds. — In  providing  for  a  continuation  of  itself  the 
following  year  the  plant  has  several  ways  of  storing  up 
food  to  be  used  before  new  roots  and  leaves  can  provide 
bodily  substance  for  the  new  plant.  Sooner  or  later  crop 
plants  bear  seeds  which  contain  carbohydrates,  oils,  and 
proteins,  all  in  the  most  concentrated  and  dehydrated 
form.  Carbohydrates  occur  in  the  form  of  starch  (Fig.  20, 
c  and  d);  and  proteins  occur  in  the  granular  or  crystalline 
form  usually  called  aleurone  grains  (Fig.  20,  b).  The  oils 
are  packed  away  as  minute  drops  (Fig.  20,  / ) .  There  is 
little  water  present  in  the  seed  (Sections  42  and  95),  and  but 
little  space  is  occupied  by  the  food  materials.  During  the 
formation  of  seeds  most  of  the  plant  activities  are  devoted 
to  the  solution  and  transportation  of  material  from  the 
leaves  and  stems,  where  it  has  been  temporarily  lodged, 
to  the  seeds,  where  it  is  changed  to  the  insoluble  form  and 
packed  away.  Dextrose  is  dehydrated  and  made  into 
starch,  or  reduced  and  made  into  oils;  in  some  cases  largely 
starch,  as  in  cereals,  in  others  largely  oils,  as  in  cottonseed. 
Peptones  and  proteoses  are  dehydrated  and  made  into 
proteins. 

74.  Roots,  Bulbs,  and  Tubers. — Some  plants  do  not  bear 
seeds  the  first  year,  but  go  into  a  resting  stage  for  a  time  and 
the  following  year  produce  seed.  These  are  the  so-called 
biennials.  To  get  a  start  the  second  year  they  must  have  a 
store  of  material  from  which  to  build  new  plant  substance 
before  roots  and  leaves  can  do  their  work.  Consequently 
they  form  enlarged  fleshy  roots,  like  the  beet;  underground 
stems  or  tubers,  like  the  potato;  or  enlarged  stalks  called 
bulbs,  like  the  onion.  In  these  storage  organs  the  car- 
bohydrates, oils,  and  proteins  are  not  usually  packed  away 
in  a  dry,  concentrated  form.  In  the  beet  carbohydrates 
take  the  form  of  sucrose;  in  the  onion,  of  dextrose;  but  in 
the  potato,  of  starch.  Oils  and  proteins  are  not  present  to 
any  extent.  If  the  latter  are  present,  however,  they  occur 
not  as  aleurone  grains,  but  in  a  more  hydrolyzed  form,  even 


UTILIZATION  OF  PLANT  FOOD 


93 


o%<?.%"o  ?qTO  O^'^'^fe'' 


'0  o 


<^oo  o' 


y  ^0  c\oqo^  o&~ 


Fig.   19 


Fig.  20 


Fig. 


Figs.  19  and  20. — Section  of  corn  kernel. 
19. — Across  the  whole  kernel.     MagniSed.    a,  epidermis;  b,  layer  of 


cells  containing  protein;  c,  hard  starch  cells;  d,  soft  starch  cells;  e,  plumule; 
/,  cotyledon  or  "germ;"  g,  primary  root. 

Fig.  20. — Detail  of  various  parts  of  kernel.  Much  magnified,  a,  epi- 
dermis; b,  cells  containing  protein  or  aleurone  grains;  c,  hard  starch  cells; 
d,  soft  starch  cells;  /,  cells  containing  oil  drops.  Lettering  to  correspond 
to  Fig.  19.     Drawing  by  C.  A.  Smith. 


94  GROWTH  OF  THE  PLANT 

amides,  etc.  Another  class  of  plants  is  called  perennials, 
which  live  on  from  year  to  year,  bear  seeds  from  time  to 
time,  and  also  maintain  life  by  means  of  succulent  storage 
organs.  Trees  are  plants  of  this  kind.  Their  reserve  car- 
bohydrates and  other  material  are  stored  just  under  the 
bark  in  the  so-called  cambium  layer. 


in.    FUNCTIONS  OF  THE  ESSENTIAL  ELEMENTS 

75.  Value  of  a  Study  of  These  Functions. — In  the  previous 
discussion  of  plant  growlh  something  has  been  said  about 
how  the  principal  plant  compounds  are  manufactured, 
but  only  in  part  has  been  noted  the  specific  function  played 
by  each  of  the  essential  elements  in  this  process. 

A  study  of  the  physiological  function  of  each  of  the  essential 
elements  is  of  practical  importance  in  the  proper  feeding 
of  a  crop  with  fertilizers.  It  is  possible  by  judicious  feeding 
to  produce  special,  desirable  results,  and  the  more  facts 
known  about  the  effect  of  fertilizers,  the  more  economically 
can  they  be  applied.  As  yet  our  knowledge  of  the  subject  is 
not  very  extensive,  although  some  progress  has  been  made. 

76.  Carbon. — This  element  is  the  principal  constituent 
(45  per  cent.)  of  the  dry  matter  of  plants.  All  of  the  com- 
pounds manufactured  by  plants  contain  carbon.  Every 
naturally  occurring  organic  compound  owes  its  carbon  content 
directly  or  indirectly  to  the  activity  of  plants.  Whether 
these  compounds  are  tissues  of  the  animal  body,  or  coal 
and  oil  in  the  earth,  all  of  them  are  originally  from  plants. 
Animals  use  as  food  either  other  animals  or  plants,  and  thus 
directly  or  indirectly  are  dependent  on  plants  as  the  source 
of  carbon.  Coal  and  oil  in  the  earth  are  decomposed  remains 
of  plants.  The  very  numerous  "coal  tar  derivatives"  were 
originally  plant  compounds,  decomposed  in  part  by  heat 
and  pressure  within  the  earth,  in  part  by  the  chemist. 

77.  Hydrogen. — This  is  another  of  the  elements  which  is  an 
essential  constituent  of  plant  compounds.  Every  organic  com- 
pound in  plants,  except  neutral  oxalates,  contains  hydrogen. 
And  yet  in  spite  of  its  wide  distribution,  plants  average  only 


FUNCTIONS  OF  THE  ESSENTIAL  ELEMENTS        95 

6.5  per  cent,  of  hydrogen.    This  is  because  of  its  extreme 
lightness,  being  the  Hghtest  of  all  the  elements. 

78.  Oxygen. — This  element  is  second  to  carbon  as  a 
constituent  of  the  dry  matter  of  plants,  occurring  to  the 
extent  of  42  per  cent.,  and  entering  into  the  composition 
of  most  plant  compounds.  In  addition  it  is  necessary  for 
respiration,  or  for  the  oxidation  of  material,  which  results 
in  energy  for  the  growing  plant  (Section  65).  Combined 
with  hydrogen  it  forms  water  which  may  be  considered 
here  with  respect  to  its  physiological  functions,  although 
it  is  not  an  element. 

79.  Water. — ^This  compound  serves  a  variety  of  purposes 
in  the  plant,  (a)  It  provides  a  medium  in  which  plant  food 
is  dissolved  and  by  which  food  can  be  transported  through- 
out the  plant.  (6)  It  is  a  reagent  which  helps  break  down 
insoluble  compounds  to  form  soluble  compounds  (Sections 
42,  63,  and  70).  (c)  By  filling  the  cells  and  pressing  against 
their  walls,  it  gives  rigidity  to  the  plant  structure  and  keeps 
it  erect.  This  filling  out  of  the  cells  is  called  "turgor." 
(d)  By  its  evaporation  from  the  leaves,  water  reduces  the 
temperature  of  plants  and  thus  prevents  overheating  due 
to  the  sun's  rays. 

80.  Phosphorus. — (a)  As  a  necessary  constituent  of  some 
proteins  phosphorus  is  required  for  the  building  up  of 
certain  plant  compounds.  Cell  nuclei,  for  example,  contain 
phosphorus.  Hence  this  element  is  necessary  for  cell  division 
and  new  growth.  (6)  It  stimulates  the  growth  of  seedlings 
markedly.  This  is  to  be  noted  in  the  practice  of  drilling  a 
soluble  phosphate  with  corn.  Although  they  did  not  know 
it,  it  was  also  the  cause  of  better  corn  growth  when  the  early 
New  England  Indians  planted  a  dead  fish  in  each  hill,  and 
so  advised  the  Pilgrims,  (c)  Phosphorus  is  important  in  the 
ripening  of  grain.  A  plentiful  supply  hastens  maturity  and 
also  increases  the  yield  of  grain  over  straw  or  stover  (Fig.  21). 
(d)  A  plentiful  supply  of  available  phosphorus  in  the  soil 
increases  root  growth.  This  increase  in  root  growth  is 
important  for  crops,  especially  during  a  dry  season  when  a 
generous  root  system  permits  plants  to  get  subsoil  water 
more  easily.    This  fact  has  been  noticed  particularly  in  the 


96 


GROWTH  OF  THE  PLANT 


growth  of  cereals  in  South  AustraHa.    (e)  Plenty  of  phos- 
phorus reduces  the  content  of  nitrogen  in  seeds  of  grains. 


Fig.  21. — Effect  of  phosphorus  on  seed  development.  Corn.  The  shock 
on  the  right  came  from  a  phosphate-treated  plat.  (Soils  Department 
Wisconsin  Station.) 

81.  Potassium. — (a)  For  the  manufacture  of  carbo- 
hydrates, potassium  is  necessary.  It  seems  probable  that 
the  condensation  of  formaldehyde  to  dextrose  takes  place 
only  in  the  presence  of  some  potassium  compound,  organic 
in  nature.  (6)  For  the  hydrolysis  of  starch,  potassium 
seems  necessary,  possibly  forming  a  suitable  solution  in 
which  the  amylases  can  best  act.  (c)  The  presence  of  potas- 
sium is  necessary  for  the  production  of  cellulose,  since  it 
gives  rigidity  to  stems.     A  lack  of  potassium  is  shown  in 


Fig.  22 


Fig.  23 
Fios.  22  and  23. — Effect  of  potassium  on  development  of  roots  containing 
carbohydrate.    Sugar  beets.    KPN,  potassium,  phosphorus,  nitrogen.    PN, 
phosphorus,  nitrogen. 
7 


98  GROWTH  OF   THE  PLANT 

weak,  brittle  stems,  where  there  is  insufficient  cellulose  for 
the  cell  walls.  Potassium  helps  the  plant  to  resist  attacks 
of  fungous  diseases  such  as  the  rust.  Fungous  hyphae  can 
not  readily  penetrate  strong  cell  walls,  (d)  It  serves  also 
to  cause  good  leaf  development,  (e)  It  gives  enlarged 
yields  of  potatoes,  which  are  a  starchy  crop.  (/)  It  also 
increases  the  yield  of  sugar  in  beets  (Figs.  22  and  23). 
This  is  very  well  illustrated  at  the  Rothamsted  Station, 
England,  w^here  a  mangold  crop  fertilized  with  nitrogen  and 
phosphorus  produced  1594  pounds  of  sugar,  but  when  fertil- 
ized with  potassium,  in  addition  to  nitrogen  and  phosphorus, 
produced  4446  pounds,  (g)  Potassium  also  is  the  base  which 
neutralizes  or  partly  neutralizes  the  acids  produced  during 
plant  growth. 

82.  Nitrogen. — (a)  Nitrogen  is  a  necessary  constituent 
of  all  proteins,  and  proteins  play  a  very  considerable  part 
in  the  formation  of  protoplasm,  chlorophyl,  and  many  other 
compounds  (Section  72).  (b)  It  is  important  in  the  growth 
of  new  tissue,  such  as  stems  and  leaves  (Fig.  24),  producing 
a  bright  green  color  in  the  leaves  (effect  on  chlorophyl). 
In  case  an  excess  is  present  such  a  vigorous  growth  of  foliage 
is  produced  as  to  delay  maturity  of  the  seed.  The  ripening 
of  the  seed  is  a  process  of  translocation  of  food  material 
which  does  not  take  place  while  active  assimilation  and 
vegetative  growth  are  going  on.  This  effect  of  delaying 
maturity  is  just  the  opposite  of  the  effect  of  phosphorus  which 
hastens  it.  (c)  Excess  of  nitrogen  also  causes  such  rapid 
vegetative  growth  that  the  stems  are  weakened,  and  lodging 
in  the  case  of  grain  may  result.  Apparently  the  cells  of  the 
growing  stem  are  multiplied  more  rapidly  than  proper  cell 
walls  can  form,  and  large  cells  with  weakened  walls  result. 
(d)  In  the  case  of  leafy  crops,  such  as  lettuce  and  cabbage, 
or  of  a  stem  crop  like  celery,  this  excess  of  nitrogen  is 
advantageous.  Seeds  are  not  wanted,  (e)  This  effect  of 
too  much  nitrogen  on  growth  renders  plants  susceptible  to 
disease.  Wheat  crops  over-stimulated  with  nitrogen  are 
liable  to  rust.  Greenhouse  crops  which  are  always  grown 
on  soils  rich  in  nitrogen  are  peculiarly  sensitive  to  diseases. 
Shrubbery  and  young  trees  which  have  been  forced  too 


FUNCTIONS  OF  THE  ESSENTIAL  ELEMENTS        99 

rapidly  with  nitrogen  are  also  more  easily  attacked  by  fungi. 
The  cause  is  due  not  only  to  a  cell  wall  less  resistant  to  the 
passage  of  the  fungous  hyphse,  but  also  in  all  probability 
to  a  change  in  the  composition  of  the  cell  sap  which  is  more 
favorable  to  the  growth  of  the  fungi. 


Fig.  24.- 


-Eflfect  of  nitrogen  on  leaf  development.    Rape. 
Jar  12,  nitrate.    Wisconsin  Station. 


Jar  5,  no  nitrate 


83.  Sulphur. — (a)  This  is  a  necessary  constituent  of  most 
proteins.  (6)  It  is  also  a  part  of  some  of  the  flavoring  oils 
in  mustard,  onion,  cabbage,  and  horseradish. 

84.  Calcium. — (a)  Like  potassium,  calcium  has  some 
part  to  play  in  the  solution  and  transportation  of  starch, 
probably  by  forming  a  proper  medium  for  the  activity 
of  the  amylases.  (6)  It  also  takes  part  in  the  development 
of  strong  cell  walls,  and  numerous  root  hairs,  (c)  It  serves 
as  a  base  to  precipitate  oxalic  acid  which  is  formed  during 
respiration  and  some  other  activities  (Section  69),  and  which 
is  poisonous  to  the  plant  if  allowed  to  accumulate.  Crystals 
of  calcium  oxalate  occur  frequently  in  plants  (Fig.  17,  d). 


100  GROWTH  OF  THE  PLANT 

(d)  It  is  also  supposed  to  be  a  necessary  constituent  of  the 
proteins  of  the  cell  nuclei. 

85.  Iron. — This  element  is  necessary  for  the  manufacture 
of  chlorophyl,  although  not  a  constituent  part  of  the  ehloro- 
phyl  compound.  Plants  which  fail  to  absorb  iron,  or  which 
do  not  absorb  enough  to  keep  pace  with  growth,  produce 
white  leaves,  a  diseased  condition  known  as  chlorosis. 

86.  Magnesium. — (a)  The  production  of  chlorophyl  is 
dependent  on  magnesium,  which  is  a  necessary  constituent. 
(b)  Protein  formation  is  helped  by  this  element,  and  par- 
ticularly in  the  assimilation  of  phosphorus,  (c)  The  forma- 
tion of  seeds  is  also  dependent  on  the  activity  of  magnesium, 
possibly  as  a  carrier  of  phosphorus  in  the  plant. 

87.  General  Distribution  in  Seed  Crops. — The  staple  crops 
in  agriculture  are  the  grains,  typical  seed  plants,  which 
are  of  value  both  for  their  seeds  and  for  their  stems  and 
leaves.  The  distribution  of  the  essential  elements,  and 
particularly  of  the  fertilizing  elements,  in  such  plants  is  of 
importance,  not  only  in  connection  with  their  physiological 
functions,  but  also  with  respect  to  their  use  on  the  soil  and 
their  economic  value.  Carbon,  hydrogen,  and  oxygen  need 
not  be  considered. 

Taking  the  mature  plant  as  harvested,  it  is  to  be  noted 
that  phosphorus  and  nitrogen  move  to  the  seeds  during 
ripening  to  such  an  extent  that  there  are  two  to  three  times 
as  much  phosphorus  and  nitrogen  in  the  seeds  as  in  the 
leaves  and  stems.  Potassium  and  calcium,  on  the  other 
hand,  being  necessary  parts  of  the  assimilating  mechanism, 
remain  in  the  stems  and  leaves  where  two  to  three  times  as 
much  potassium,  and  nearly  eight  times  as  much  calcium, 
are  found  as  in  the  seeds.  Sulphur  is  more  evenly  dis- 
tributed, being  a  trifle  more  in  the  stems  and  leaves  than 
in  the  seeds,  except  in  the  corn  plant.  Iron,  being  necessary 
for  the  formation  of  chlorophyl,  is  found  in  the  leaves  and 
stems  to  a  greater  extent  than  in  the  seeds.  Magnesium 
is  more  evenly  distributed,  with  a  trifle  more  in  the  seeds 
than  in  the  stems  and  leaves  of  most  grains  except  corn. 

For  the  distribution  of  fertilizing  constituents  in  fruits  and 
vegetables  the  reader  is  referred  to  Table  III,  Chapter  IV. 


REFERENCES  101 

The  commercially  valuable  part  of  these  crops  differs  with 
the  kind  of  plant,  thus  making  any  general  discussion 
impossible.  For  example,  the  apple,  pear,  squash,  and  pump- 
kin are  raised  for  the  fleshy  seed  coverings;  celery  and  rhubarb 
for  their  thickened  stems;  the  carrot  and  beet  for  their 
thickened  root;  and  spinach  and  lettuce  for  their  leaves. 

EXERCISES 

1.  In  detail  show  the  relation  that  exists  between  oxidation  within  the 
plant  cell  and  photosynthesis. 

2.  Starting  with  carbon  dioxide,  water,  nitrates,  phosphates  and  sulphates 
build  up  the  following  compounds:  Dextrose,  maltose,  sucrose,  starch, 
cellulose,  lignin,  protein,  fat.  In  doing  so,  show  that  dextrose  is  the  initial 
organic  substance  formed  by  the  plant  for  the  elaboration  of  other  organic 
substances. 

3.  What  are  the  intermediate  and  end-products  of  the  hydrolysis  of 
starch,  fat  and  proteins  in  a  plant? 

4.  Compare  hydrolysis  and  condensation  physically,  chemically,  and  as 
to  their  function  in  plants. 

5.  What  is  the  purpose  of  oxidation  in  the  plant?  Name  the  three  prod- 
ucts usually  formed  by  such  action.     Which  one  is  of  use  to  the  plant? 

6.  What  do  the  following  prefixes  and  suffixes  mean:  yl,  ase,  ose,  ide,  ate, 
ol,  um?     Do  they  usually  or  always  hav^e  this  meaning? 

7.  Name  the  ten  essential  plant  elements.  In  four  words  describe  the  form 
in  which  they  are  absorbed.  What  part  does  the  protoplasmic  lining  of  the 
root  hairs  play  in  this  absorption? 

8.  State  why  a  good  nurse  will  take  plants  from  the  sick  room  at  night 
and  return  them  in  the  daytime. 

9.  Do  plants  breathe  oxygen?     If  so,  why? 

10.  Explain  in  detail  how  water  by  its  evaporation  from  the  leaves  of 
plants  reduces  the  temperature  of  plants  and  prevents  the  overheating 
caused  by  the  sun's  rays. 

11.  What  plant  poison  composed  only  of  carlx)n,  hydrogen  and  oxygen  is 
formed  during  plant  growth?  How  does  the  plant  prevent  its  doing  any 
damage? 

12.  If  a  substance  outside  the  root  hairs  is  soluble  and  inorganic  does 
that  mean  it  will  be  absorbed?     If  not,  why  not? 

13.  Into  what  kind  of  energy  is  the  energ>-  of  the  sun  changed  during 
photosynthesis? 

REFERENCES 

See  References  at  end  of  Chapter  II. 


CHAPTER  IV 
CROPS 

The  so-called  crop  plants — those  plants  which  are  of 
value  to  the  farmer — owe  their  importance  to  certain  of 
their  constituents.  For  example,  the  grains  are  valuable  for 
the  starch,  fixed  oils,  and  proteins,  which  they  contain; 
potatoes  for  their  starch;  nuts  for  their  oils;  peas  and  beans 
for  their  proteins;  and  beets  for  their  sugar.  Since  most  of 
the  ordinary  crop  plants  are  raised  almost  entirely  as  food 
for  stock  or  for  man,  it  is  of  interest  to  know  something  of 
the  amounts,  not  only  of  the  valuable,  but  also  of  the  useless 
food  constituents  in  the  various  crops. 

The  determination  of  the  different  individual  plant  com- 
pounds discussed  in  Chapter  I  involves  considerable 
difficulty,  and  although  many  of  the  determinations  can  be 
made  with  accuracy,  the  time  consumed  is  very  great  even 
if  only  a  partial  analysis  is  made.  For  scientific  stock 
feeding  it  is  only  necessary  to  know  the  amount  of  all  the 
carbohydrates  that  are  reasonably  digestible;  the  amount 
of  those  carbohydrates  which  are  indigestible;  the  amount 
of  total  protein  material;  of  total  oil;  and  of  total  mineral 
matter.  Consequently  there  is  employed  a  method  which 
serves  to  differentiate  the  classes  of  constituents  rather 
than  the  compounds  in  each  class. 

The  determinations  are  more  or  less  conventional  and  in 
some  cases  only  approximate,  but  on  the  whole  they  are 
reasonably  accurate.  This  general  method  of  analysis  is 
known  as  the  "Weende  Method"  since  it  was  the  method 
employed  at  the  Weende  Experiment  Station,  Germany, 
by  Dr.  W.  Henneberg,  and  reported  by  him  in  1864.  With 
some  modifications  it  is  still  in  use.  A  very  brief  description 
of  the  following  determinations  will  help  to  make  clear  the 
meaning  of  terms  which  are  referred  to  very  frequently  in 
any  discussion  of  foods. 
(102) 


CROP  CONSTITUENTS  AND  DETERMINATION     103 


I.     CROP  CONSTITUENTS  AND  THEIR  DETERMINATION 

88.  Water  or  Moisture. — ^This  is  the  loss  in  weight  of  the 
material  which  takes  place  when  it  is  dried  at  the  temperature 
of  boiling  water,  a  little  under  100°  C.  usually,  and  sometimes 
in  an  atmosphere  of  hydrogen  or  in  vacuo.  If  the  tem|x?ra- 
ture  is  lower,  not  all  of  the  water  will  be  driven  off;  if  it  is 
higher,  organic  compounds  begin  to  break  up  and  the  results 
will  be  high.  It  is  in  some  cases  necessary  to  make  the  deter- 
mination in  an  atmosphere  of  hydrogen  or  in  vacuo,  because 
many  crops  contain  "drying"  or  "semidrying"  oils,  which 
would  absorb  oxygen  if  dried  in  the  air,  and  the  results  for 
moisture  would  be  incorrect. 

89.  Crude  Fat. — ^This  constituent  is  obtained  by  extracting 
the  dried  material  with  dry,  alcohol-free  ether.  The  extract 
is  dried  carefully  at  the  temperature  of  boiling  water  to 
remove  the  ether,  and  then  weighed.  If  water  is  present 
in  the  sample,  or  if  it  is  present  in  the  ether,  or  if  alcohol 
is  present  in  the  ether,  there  is  danger  of  dissolving  some 
of  the  carbohydrates  and  ash  constituents.  Crude  fat 
consists  of  fixed  oils,  volatile  oils,  waxes,  resins,  chlorophyl, 
and  other  pigments,  if  present,  and  possibly  some  other 
ether-soluble  compounds.  This  accounts  for  the  fact  that 
it  is  called  crude  fat,  for  it  is  an  approximate  method  at  best, 
although  in  most  of  our  crop  plants  the  constituents  other 
than  fixed  oils  are  very  small  in  amount. 

90.  Crude  Fiber. — The  material  which  has  been  dried  and 
extracted  with  ether  is  boiled  first  with  dilute  sulphuric 
acid,  then  with  dilute  sodium  hydroxide,  giving  it  a  thorough 
washing  after  each  treatment.  The  amount  of  acid  and 
alkali,  as  well  as  the  strength  and  time  of  boiling  are  very 
carefully  regulated.  By  drying  and  weighing  the  residue, 
igniting  and  weighing  the  remaining  ash,  the  difference  in 
weight  will  give  the  crude  fiber  which  consists  of  cellulose, 
lignin,  and  possibly  some  proteins.  The  treatment  with 
acid  and  alkali  is  supposed  to  remove  all  soluble  sugars; 
starch  which  is  hydrolyzed  to  dextrose  and  washed  out; 
proteins  which  are  hydrolyzed  and  removed;  and  any  other 
constituents  rendered  soluble  by  these  reagents. 


104  CROPS 

91.  Ash. — By  burning  the  material  and  continuing  to 
heat  it  until  all  the  organic  matter  has  been  destroyed,  the 
weighed  residue  will  constitute  the  ash  or  the  mineral  con- 
stituents of  the  plant  substance.  These  mineral  constituents 
will  not  occur  in  the  ash  in  the  same  form  as  in  the  plant, 
for  the  bases  which  were  originally  united  with  organic  acids 
will  be  present  in  the  ash  as  sulphates,  phosphates,  silicates, 
and  carbonates.  Sulphur  and  phosphorus  in  proteins  will 
occur  here  as  sulphates  and  phosphates  of  the  bases.  Silicon, 
which  may  or  may  not  have  been  present  in  the  plant  in 
organic  combination,  will  occur  in  the  ash  as  silicates. 
The  excess  of  inorganic  basic  elements  over  inorganic  acid 
elements  will  be  present  in  the  ash  as  carbonates.  The  ash 
residue  from  the  crude  fiber  determination  will  not  serve 
in  this  determination,  since  much  of  the  inorganic  material 
has  been  removed  by  the  treatment  with  acid  and  alkali. 

92.  Crude  Protein. — By  using  a  well  known  method  for  the 
determination  of  total  nitrogen  (Section  35)  and  multiplying 
the  result  by  6.25  the  percentage  of  crude  protein  is  obtained. 
This  is  based  on  the  assumption  that  proteins  contain  on  the 
average  16  per  cent,  of  nitrogen.  The  assumption  is  only 
approximately  correct.  This  method,  however,  does  not 
take  into  consideration  the  presence  of  nitrogen  in  other 
than  protein  form.  In  some  cases  there  is  a  considerable 
amount  of  this  non-protein  nitrogen  which  is  of  importance 
in  feeding.  Consequently  it  is  customary  in  most  cases  to 
determine  the  so-called  "Albuminoid  Nitrogen"  or  protein 
nitrogen  and  calculate  this  to  proteins.  The  method  is 
based  on  the  fact  that  proteins  are  precipitated  by  copper 
hydroxide,  whereas  amides,  ammonia,  and  nitrates  are  not. 
After  washing  the  precipitate  of  proteins  and  copper 
hydroxide  the  total  nitrogen  is  determined  and  the  result 
multiplied  by  6.25  as  before.  The  difference  between  the 
total  nitrogen  and  protein  nitrogen,  is  multiplied  by  4.7 
and  called  amides,  on  the  assumption  that  amides  are 
asparagine  and  contain  21.2  per  cent,  of  nitrogen — a  very 
broad  generalization. 

93.  Nitrogen-free  Extract,  or  Digestible  Carbohydrates. — 
This  is  merely  the  difference  between  100  per  cent,  and  the 


CLASSIFICATION  AND  ANALYSES  OF  CROPS      105 

sum  of  all  the  other  constituents.  It  comprises  starch,  the 
sugars,  and  any  other  compounds  not  determined  elsewhere. 
Most  of  the  analyses  now  in  use  give  this  determination  only, 
but  it  is  customary  at  present,  in  most  work  of  a  careful 
nature,  to  make  separate  determinations  of  sucrose;  of 
reducing  sugars,  such  as  dextrose,  levulose,  and  maltose; 
of  starch;  and  of  the  pentosans. 

n.     CLASSIFICATION  AND  ANALYSES  OF  CROPS 

94.  Classification. — The  classification  of  crops  is  always 
more  or  less  arbitrary,  particularly  so  since  the  popular 
names  for  kinds  of  crops  differ  from  the  scientific  names. 
For  example,  the  botanical  term  for  the  matured  ovary  and 
its  contents  is  fruit,  no  matter  whether  the  part  of  the 
plant  in  question  belongs  to  corn,  or  walnut,  or  apple,  or 
pumpkin.  Popularly  the  term  fruit  is  restricted  to  those  soft, 
fleshy  seed  coverings  of  the  apple,  pear,  and  similar  plants. 

In  the  present  classification  an  attempt  has  been  made  to 
arrange  the  crops  in  the  main  according  to  the  part  of  the 
plant  from  which  the  money  value  is  obtained,  and  with  some 
regard  for  popular  terminology.  The  Seed  Crops  are  those 
which  are  raised  primarily  for  the  seeds  themselves,  and  they 
are  subdivided  into  Grains,  Legumes,  and  Miscellaneous. 
The  stems  and  leaves  of  the  ripe  grains  are  also  included 
here  for  comparison. 

The  Fruit  Crops  are  those  which  are  raised  for  their 
fleshy  seed  coverings  and  are  particularly  sweet. 

The  Stem  and  Leaf  Crops  or  the  Fodder  Crops  are  those 
which  are  used  only  for  the  stems  and  leaves.  In  some  cases, 
corn  fodder,  for  example,  the  crop  may  be  used  when  green 
as  fodder,  or  when  ripe  as  a  seed  crop.  The  composition  of 
these  crops  is  given  at  the  time  of  cutting,  not  when  cured 
for  hay.    For  the  latter  see  Section  101,  and  Table  IV. 

The  Vegetable  Crops  are  all  those  "garden  crops"  which 
are  popularly  called  vegetables.  They  are  valuable  for  their 
succulent  or  juicy  parts,  and  may  be  conveniently  sub- 
divided into  Stem,  Leaf,  Root,  and  Fruit  Vegetables.     It 


106 


CROPS 


is  to  be  noted  that  potatoes  are  classed  with  the  Root 
Vegetables,  although  they  are  really  underground  stems, 
not  roots. 

95.  Analyses. — ^Table  I  gives  the  percentage  composition 
of  a  number  of  crops  in  each  class.  Table  II  gives  the 
yields  in  pounds  per  acre  of  each  crop  as  a  whole,  and  of  the 
several  constituents  of  each  crop.  Table  III  gives  the  per- 
centage composition  of  these  same  crops  in  the  three  chief  fer- 
tilizing constituents — nitrogen,  phosphoric  acid,  and  potash. 


Table    I. — Percentage   Composition   of   Crops 
SEED  crops 


Nitrogen- 

Crude 

Crude 

free 

Crude 

Grains.                                Water. 

Ash. 

protein . 

fiber. 

extract. 

fat. 

Barley: 

Seed      ....      10.9 

2.4 

12.4 

2.7 

69.8 

1.8 

Straw 

14.2 

5.8 

3.5 

36.0 

39.0 

1.5 

Corn: 

Seed 

10.6 

1.5 

10.3 

2.2 

70.4 

5.0 

Stover 

22.8 

4.9 

5.5 

25.6 

39.9 

1.3 

Oats: 

Seed 

11.0 

3.0 

11.8 

9.5 

59.7 

5.0 

Straw 

9.2 

5.1 

4.0 

37.0 

42.4 

2.3 

Rye: 

Seed 

11.6 

1.9 

10.6 

1.7 

72.5 

1.7 

Straw 

7.1 

3.2 

3.0 

38.9 

46.6 

1.2 

Wheat: 

Seed 

10.5 

1.8 

11.9 

1.8 

71.9 

2.1 

Straw 

9.6 

4.2 

3.4 

38.1 

43.4 

1.3 

Legumes 

Cowpea 

14.8 

3.2 

20.8 

4.1 

55.7 

1.4 

Soja  Bean 

10.8 

4.7 

34.0 

4.8 

28.8 

16.9 

Miscellaneous. 

Cotton  Seed 

10.3 

3.5 

18,4 

23.2 

24.7 

19.9 

Flax  Seed 

9.2 

4.2 

22.6 

7.1 

23.2 

33.7 

FRUIT 

CROPS 

Nitrogen- 

Crude 

Crude 

free 

Crude 

Water. 

Ash. 

protein. 

fiber. 

extract. 

fat. 

Apples      .      .      .      .      84.6 

0.3 

0.4 

1.2 

13.0 

0.5 

Blackberries 

86.3 

0.5 

1.3 

2.5 

8.4 

1.0 

Cherries   . 

80.9 

0.6 

1.0 

0.2 

16.5 

0.8 

Currants  . 

85.0 

0.7 

1.5 

12 

.8 

Grapes 

77.4 

0.5 

1.3 

4.3 

14.9 

1.6 

Peaches    . 

89.4 

0.4 

0.7 

3.6 

5.8 

0.1 

Pears  . 

84.4 

0.4 

0.6 

2.7 

11.4 

0.5 

Raspberries,  black 

84.1 

0.6 

1.7 

12 

.6 

1.0 

Strawberr 

ies 

90.4 

0.6 

1.0 

1.4 

6.0 

0.6 

CLASSIFICATION  AND  ANALYSES  OF  CROPS      107 


Table   I— Pei 

ICENTAGE 

Compos] 

TION    OF 

Crops- 

— (Continued) 

STEM 

AND    LEAF    CROPS 

Nitrogen- 

Crude 

Crude 

free 

Crude 

Water. 

Ash. 

protein. 

fiber. 

extract. 

fat. 

Alfalfa,  green 

71.8 

2.7 

4.8 

7.4 

12.3 

1.0 

Alsike  clover,  green 

74.8 

2.0 

3.9 

7.4 

11.0 

0.9 

Corn  fodder,  green 

79.3 

1.2 

1.8 

5.0 

12.2 

0.5 

Orchard  grass,  green     73.0 

2.0 

2.6 

8.2 

13.3 

0.9 

Red  clover,  green 

70.8 

2.1 

4.4 

8.1 

13.5 

1.1 

Timothy,  green  . 

61.6 

2.1 

3.1 

11.8 

20.2 

1.2 

Alfalfa,  hay   . 

8.4 

7.4 

14.3 

25.0 

42.7 

2.2 

Alsike  clover,  hay 

9.7 

8.3 

12.8 

25.6 

40.7 

2.9 

Corn  fodder,  cured 

42.2 

2.7 

4.5 

14.3 

34.7 

1.6 

Orchard  grass,  hay 

9.9 

6.0 

8.1 

32.4 

41,0 

2.6 

Red  clover,  hay 

15.3 

6.2 

12.3 

24.8 

38.1 

3.3 

Timothy,  hay 

13.2 

4.4 

5.9 

29.0 

45.0 

2.5 

VEGETABLE    CROPS 

Nitrogen- 

Crude 

Crude 

free 

Crude 

Water. 

Ash. 

protein. 

fiber. 

extract. 

fat. 

Stem  vegetables: 

Asparagus 

94.0 

0.7 

1.8 

0.8 

2.5 

0.2 

Celery  . 

94.5 

1.0 

1.1 

3.3 

0.1 

Rhubarb    . 

94.4 

0.7 

0.6 

1.1 

2.5 

0.7 

Leaf  vegetables: 

Cabbage     . 

91.5 

1.0 

1.6 

1.1 

4.5 

0.3 

Lettuce 

94.7 

0.9 

1.2 

0.7 

2.2 

0.3 

Onions 

87.6 

0.6 

1.6 

0.8 

9.1 

0.3 

Spinach 

92.3 

2.1 

2.1 

0.9 

2.3 

0.3 

Root  vegetables: 

Beets    .      .      . 

87.5 

1.1 

1.6 

0.9 

8.8 

0.1 

Carrots 

88.2 

1.0 

1.1 

1.1 

8.2 

0.4 

Parsnips     . 

83.0 

1.4 

1.6 

2.5 

11.0 

0.5 

Potatoes     . 

78.3 

1.0 

2.2 

0.4 

18.0 

0.1 

Turnips 

89.6 

0.8 

1.3 

1.3 

6.8 

0.2 

Fruit  vegetables: 

Cucumbers 

95.4 

0.5 

0.8 

0.7 

2.4 

0.2 

Squash 

88.3 

0.8 

1.4 

0.8 

8.2 

0.5 

Tomatoes  . 

94.3 

0.5 

0.9 

0.6 

3.3 

0.4 

Watermelons  . 

92.4 

0.3 

0.4 

6.7 

0.2 

It  also  gives  the  yields  of  these  constituents  in  pounds  per 
acre.  This  latter  part  of  the  table  illustates  the  distribution 
of  these  essential  elements  as  discussed  in  Section  87.  The 
seed  and  fodder  crops  are  reported  as  harvested ;  the  fodder 
crops  also  as  cured.  Fruit  and  vegetable  crops  are  reported 
on  the  edible  portion  only,  except  for  blackberries,  currants, 
asparagus,  spinach,  and  tomatoes  which  are  reported  as 
purchased.  The  yields  of  the  fruit  and  vegetable  crops 
have  also  been  calculated  to  the  edible  portion,  except  in 


108 


CROPS 


the  cases  just  mentioned.  In  the  case  of  the  analyses  of 
nitrogen,  phosphoric  acid,  and  potash,  all  crops  are  reported 
as  harvested,  except  cherries,  peaches,  and  squash,  which 
are  reported  as  edible  portion.  Here  the  yields  of  only  these 
two  crops  are  calculated  on  this  basis,  otherwise  as  harvested. 

Table  II — Yield  of  Crops  (In  Pounds  per  Acre) 

SEED    CROPS 

Nltrogen- 
At  Dry  Crude     Crude         free       Crude 

Grain.  harvest.       matter.    Ash.    protein,     fiber.       extract.      fat. 


Barley  (35  bush 

3ls): 

Seed      .      . 

.      .      1,680 

1,497 

40 

208 

46 

1,173 

30 

Straw    . 

.      .      3,000 

2,574 

174 

105 

1,080 

1,170 

45 

Corn  (50  bushels) : 

Seed      .      . 

.      .      2,800 

2,503 

42 

288 

62 

1,971 

140 

Stover  . 

.      .      2,500 

1,930 

122 

138 

640 

998 

32 

Oats  (40  bushels) : 

Seed      .      . 

.      .      1.280 

1,139 

38 

151 

122 

764 

64 

Straw    . 

.      .      1,800 

1,634 

92 

72 

666 

763 

41 

Rye  (20  bushels) 

Seed      .      . 

.      .       1,120 

990 

21 

119 

19 

812 

19 

Straw    . 

.      .      2,200 

2,044 

70 

66 

856 

1,025 

27 

Wheat  (20  bushels) : 

Seed      .      . 

1,200 

1,074 

22 

143 

22 

862 

25 

Straw    . 

.      .      2,000 

1,808 

84 

68 

762 

868 

26 

Legumes. 

Cowpea  (20  bu.) 

1,200 

1,022 

38 

250 

49 

668 

17 

Soja  Bean  (20  bu.)          1,200 

1,070 

56 

408 

58 

345 

203 

Miscellaneous. 

Cotton  Seed 

850 

762 

30 

156 

197 

210 

169 

Flax  Seed 

560 

509 

23 

127 

40 

130 

189 

FRUIT   CROPS 

Nitrogen- 

At 

Dry 

Crude 

Crude 

free 

Crude 

harvest. 

matter. 

Ash. 

proteir 

.     fiber. 

extract. 

fat. 

Apples 

.     18.750 

2.888 

56 

75 

225 

2,438 

94 

Blackberries 

3,000 

411 

15 

39 

75 

252 

30 

Cherries 

3,800 

726 

23 

38 

8 

627 

30 

Currants 

4,000 

600 

28 

60 

512 

Grapes 

6,000 

1,356 

30 

78 

258 

894 

96 

Peaches 

.    30,750 

3,260 

123 

215 

1,107 

1,784 

31 

Pears 

.    27,000 

4,212 

108 

162 

729 

3,078 

135 

Raspberries 

2,850 

453 

17 

48 

359 

29 

Strawberries 

.      5,700 

547 

34 

57 

80 

342 

34 

STEM    AND    LEAF 

CROPS 

CURED 

Alfalfa 

.      10,000 

9,160 

740 

1,430 

2,500 

4,270 

220 

Alsike  clover 

5,000 

4,515 

415 

640 

1,280 

2,035 

145 

Corn  fodder 

.    20,000 

11,560 

540 

900 

2,860 

6,940 

320 

Orchard  grass 

4,000 

3,604 

240 

324 

1,296 

1.640 

104 

Red  clover 

5,000 

4.235 

310 

615 

1,240 

1,905 

165 

Timothy     . 

5,000 

4.340 

220 

295 

1.450 

2,250 

125 

CLASSIFICATION  AND  ANALYSES  OF  CROPS     109 


Table  II — Yield  of  Crops — (Continued) 


VEOETABLE    CROPS 


At 

Dry 

Crude 

Crude 

Nitrogen- 
free 

Crude 

harvest. 

matter. 

Ash. 

protein. 

fiber. 

extract. 

fat. 

Stem  vegetables: 

Asparagus 

4.000 

240 

28 

72 

32 

100 

8 

Celery  . 

8,000 

440 

80 

88 

264 

8 

Rhubarb    . 

12,000 

672 

84 

72 

132 

300 

84 

Leaf  vegetables: 

Cabbage     . 

25,500 

2,167 

255 

408 

281 

1,147 

76 

Lettuce 

12.750 

676 

115 

153 

89 

281 

38 

Onions 

21,600 

2,678 

130 

346 

172 

1,965 

65 

Spinach 

10.000 

770 

210 

210 

90 

230 

30 

Root  vegetables: 

Beets    .      .      . 

13.440 

1,680 

148 

215 

121 

1,182 

14 

Carrots 

10,000 

1,180 

100 

110 

110 

820 

40 

Parsnips     . 

12,000 

2,040 

168 

192 

300 

1,320 

60 

Potatoes     . 

9,600 

2,083 

96 

211 

38 

1,728 

10 

Turnips 

12.600 

1,310 

101 

164 

164 

856 

25 

Fruit  vegetables: 

Cucumbers 

10.625 

489 

54 

85 

74 

255 

21 

Squash 

9,000 

1,053 

72 

126 

72 

738 

45 

Tomatoes  . 

24.000 

1,368 

120 

216 

144 

792 

96 

Watermelons  . 

9.744 

741 

30 

39 

652 

20 

Table  III — Fertilizing  Constituents  of  Various  Crops 

Percentage  composition.  Pounds  per  acre. 

N  P.06  K.0  N  P.Os  KsO 
Barley: 

Seed      ....  1.75  0.75  0.50  29.4  12.6  8.4 

Straw    ....  0.60  0.20  1.10  18.0  6.0  33.0 
Corn: 

Seed      ....  1.65  0.65  0.40  46.2  18.2  11.2 

Stover  ....  1.04  0.29  1.40  26.0  7.3  35.0 
Oats: 

Seed      ....  2.00  0.80  0.60  25.6  10.2  7.7 

Straw    ....  0.60  0.20  1,25  10.8  3.6  22.5 
Rye: 

Seed      ....  1.70  0.85  0.60  19.0  9.5  6.7 

Straw    ....  0.50  0.30  0.85  11.0  6.6  18.7 
Wheat: 

Seed      ....  2.00  0.85  0.50  24.0  10.2  6.0 

Straw    ....  0.50  0.15  0.60  10.0  3.0  12.0 

Cowpea    .      .      .      .3.10  1.00  1.20  37.2  12.0  14.4 

Sojabean       .      .      .  5.30  1.80  2.00  63.6  21.6  24.0 

Cottonseed  .      .      .  3.15  1.25  1.15  26.8  10.6  9.8 

Flaxseed        .      .      .  4.35  1.60  0.95  24.4  9.0  5.3 

Apples  (fruit)      .      .  0.05  0.02  0.10  12.5  5.0  25.0 

Blackberries  (fruit)  .  0.22  0.06  0.23  6.6  1.8  6.9 

Cherries  (fruit  pulp)  0.17  0.04.  0.20  6.5  1.5  7.6 

Currants  (fruit)  .      .  0.30  0.12  0.30  12.0  4.8  12.0 

Grapes  (fruit)      .      .  0.15  0.07  0.30  12-0  5.6  34.0 


110 


CROPS 


Table  III — Fertilizing  Constituents — (Continued) 

Percentage  composition.  Pounds  per  acre. 

N  P.Os  K2O              N  P2O6  KjO 

Peaches  (fruit  pulp)       0.08  0.04  0.20  24.6  12.3  61.5 

Pears  (fruit)         .      .      0.05  0.02  0.10  15.0           6.0  30.0 

Raspberries  (fruit)    .      0.20     •    0.10  0.25  6.0           3.0  7.5 

Strawberries  (fruit)        0.15  0.06  0.25  9.0           3.6  15.0 

Alfalfa  (green)     .      .      0.60  0.15  0.50  60.0  15.0  50.0 

Alsike  clover  (green)      0.50  0.12  0.30  25.0           6.0  15.0 

Corn  fodder  (green)       0.41  0.15  0.33  82.0  30.0  66.0 

Orchard  grass  (green)    0.45  0.15  0.55  18.0           6.0  22.0 

Red  clover  (green)    .     0.55  0.13  0.50  27.5           6.5  25.0 

Timothy  (green)  .  0.50  0.25  0.75  25.0  12.5  "  37.5 
Asparagus  (young 

shoots)        .      .      .      0.35  0.10  0.25  14.0  4.0  10.0 

Celery       ....      0.25  0.20  0.75  25.0  20.0  75.0 

Rhubarb  .      .      .      .0.10  0.04  0.35  20.0           8.0  70.0 

Cabbage  (head)         .      0.30  0.10  0.40  90.0  30.0  120.0 

Lettuce     ....      0.25  0.08  0.45  37.5  12.0  67.5 

Onions      ....      0.23  0.09  0.22  55.2  21.6  52.8 

Spinach    ....      0.50  0.15  0.25  50.0  15.0  25.0 

Beets 0.25  0.10  0.50  42.0  16.8  84.0 

Carrots     ....      0.23  0.13  0.53  28.8  16.3  66.3 

Parsnips  ....      0.22  0.20  0.65  33.0  30.0  97.5 

Potatoes  ....      0.35  0.15  0.50  42.0  18.0  60.0 

Turnips    ....      0.25  0.10  0.45  45.0  18.0  81.0 

Cucumbers  .  .  .0.10  0.06  0.20  12.5  7.5  25.0 
Squash  (edible 

portion)      .      .      .      0.22  0.08  0.05  18.0  7.2  4.5 

Tomatoes       .      .      .      0.20  0.07  0.35  48.0  16.8  84.0 

Watermelons       .      .      0.17  0.06  0.30  40.8  14.4  72.0 


in.     CROP  CHEMISTRY 

96.  Seed  Crops. — As  a  class  the  seeds  of  the  seed  crops 
are  relatively  low  in  water,  about  10  per  cent.  During  the 
process  of  seed  formation  the  soluble  sugars  are  transported 
to  the  seed  where  dehydration  takes  place  in  the  deposition 
of  starch.  This  extra  water  is  eliminated  during  the  drying 
or  curing  of  seeds.  The  same  change  of  hydrolyzed  com- 
pounds to  dehydrated  compounds  takes  place  in  the  case 
of  proteins  (Section  73).  The  leaves  and  stems  of  seed 
crops  are  also  low  in  water  inasmuch  as  they  have  dried  out 
and  are  practically  dead  before  they  are  harvested.  The 
seeds  are  low  in  ash,  much  lower  than  any  other  part  of  the 
plant.  Considered  from  the  standpoint  of  plant  economy 
the  seeds  need  very  little  of  the  mineral  elements.  Food 
for  the  seedling  is  ready  made  in  the  seed,  only  needing 


CROP  CHEMISTRY  111 

solution  to  make  it  immediately  available.  By  the  time 
the  seedling  rises  into  the  light  where  it  can  begin  the 
manufacture  of  food,  the  roots  have  begun  to  absorb  from 
the  soil  necessary  quantities  of  inorganic  elements  for  the 
synthetic  processes.  Straw  and  stover,  on  the  other  hand, 
are  high  in  ash  which  consists  largely  of  the  unessential 
element  silicon  together  with  lime  and  potash.  The  stems 
and  leaves,  it  will  be  remembered  (Section  87),  are  the  seat 
of  synthetic  processes  requiring  the  help  of  mineral  elements. 

Compared  to  other  crops,  seeds  are  high  in  crude  protein, 
crude  fat  and  nitrogen-free  extract,  or  carbohydrates,  as 
would  be  expected,  since  these  are  the  stored  foods  for  the 
next  generation.  The  carbohydrates  are  chiefly  starch. 
Straw  and  stover,  on  the  other  hand,  are  very  high  in  crude 
fiber,  which  goes  to  make  cell  walls  and  strengthening  fibers, 
not  living  matter. 

(a)  Grains. — Considering  the  grains  separately,  it  is  to 
be  noted  that  barley  seed  is  of  importance  chiefly  for  its 
nitrogen-free  extract — starch — and  the  very  active  starch 
splitting  enzyme,  diastase,  which  is  produced  on  germination. 
These  are  made  use  of  in  the  malting  of  barley  and  the  sub- 
sequent "mashing."  Barley  grains  are  soaked  in  water 
and  allowed  to  germinate.  This  results  in  the  evolution  of 
heat  (Section  43)  and  the  production  of  diastase  in  large 
quantities.  All  seeds  during  germination  produce  diastase 
of  some  kind  to  dissolve  the  starch  (Section  47),  but  barley 
diastase  is  particularly  active.  When  the  sprouts  have  well 
started  they  are  killed  by  heat  and  removed,  appearing  on 
the  market  as  "malt  sprouts,"  a  feeding  stuff.  The  barley 
grains,  now  called  malt,  are  still  very  rich  in  starch  but  have 
in  addition  quantities  of  diastase.  The  malt  is  next  heated 
with  water  when  the  diastase  converts  the  starch  to  maltose, 
a  process  called  mashing.  Diastase  can  act  on  the  starch 
of  other  grains  as  well  as  on  that  of  barley,  and  in  brewing 
it  is  used  for  the  hydrolysis  of  large  amounts  of  corn  starch. 
The  maltose  is  removed  in  solution,  and  fermented  with 
yeast,  producing  beer.  The  grain  that  is  left  behind  is  sold 
as  "brewers'  grains"  for  feeding  purposes.  The  presence  of 
much  protein  in  the  seed  interferes  with  the  malting  process. 


112 


CROPS 


Corn  seed  is  rich  in  starch  and  fat.  The  starch  is  used 
as  such,  or  converted  into  glucose  (Section  3).  The  fat  is 
extracted  and  forms  corn  oil  (Section  20,  6).  Sweet  corn 
contains  a  considerable  portion  of  its  carbohydrate  in  the 
form  of  sucrose.    Corn  is  low  in  ash. 

Oat  seed  is  higher  in  crude  fiber  and  ash  than  the  other 
grain  seeds  due  to  its  very  considerable  hull.  It  is  corre- 
spondingly lower  in  digestible  carbohydrates.  The  proportion 
of  fat  is  also  high,  being  equalled  only  by  that  of  corn. 

Rye  seed  has  a  relatively  low  protein  content  like  corn 
seed,  and  is  low  in  fat  like  barley. 


Fig.  25. 


-Seed  crop:    Wheat.     Agronomy  Depuriim'in,  i^'onsjlvaiiia 
Station. 


Wheat  seed  (Fig.  25)  has  no  particularly  noticeable  con- 
stituent as  far  as  percentage  goes.  Its  starch  is  the  chief 
constituent  of  flour  and  one  of  its  proteins  deserves  particular 
mention  in  this  connection.  It  is  a  protein  called  gliadin,  to 
which  wheat  flour  owes  its  stickiness  or  tenacity  when  mixed 
with  water,  and  on  which  the  baking  qualities  depend,  serving 
to  keep  the  baked  loaf  light.  Carbon  dioxide  formed  by  the 
yeast  puffs  out  the  sticky  mass  into  many  minute  cells,  the 


CROP  CHEMISTRY 


113 


gliadin  giving  tenacity  to  the  cell  walls.  If  it  were  not  for 
the  gliadin  the  mass  would  be  solid  and  hard.  This  is  the 
case  with  flour  from  other  grain  seeds  containing  no  gliadin, 


114  CROPS  - 

or  at  least  not  enough  to  give  good  baking  quality  to  bread 
made  from  them. 

The  straws  from  these  grains  are  not  as  a  class  very 
digestible,  except  possibly  barley  and  oats.  The  ash  is  high 
in  silica  and  potash. 

(6)  Legumes. — ^These  seeds  are  particularly  high  in  protein 
and  correspondingly  low  in  carbohydrates.  The  soja  bean 
contains  considerable  fat. 

(c)  Miscellaneous. — CottonSeedandFlaxSeed(Fig.  26) are 
very  high  in  fat  and  are  used  for  the  oil  which  can  be  expressed 
from  them  (Section  20,  c  and  d).  The  press  cake  is  used  as 
a  feeding  stuff  and  fertilizer  on  account  of  its  high  nitrogen 
content.  These  seeds  are  also  high  in  fiber  and  very  low 
in  carbohydrates. 

97.  Fruit  Crops  (Fig.  27). — ^These  crops  are  remarkable 
for  the  extremely  large  amounts  of  water  which  they  contain. 
A  pound  of  peach  pulp  or  of  strawberries,  for  example, 
contains  more  water  than  a  pound  (approximately  pint)  of 
milk.  It  is  this  water  content  which  makes  fruit  such  a 
valuable  addition  to  the  ordinary  forms  of  food.  The  dry 
matter  of  fruits  contains,  in  some  cases  about  as  much  protein 
as  the  grains,  in  most  cases  more  crude  fiber,  in  many  cases 
more  nitrogen-free  extract.  When  the  fruit  is  green,  the 
nitrogen-free  extract  consists  largely  of  starch,  which  is 
converted  to  such  soluble  sugars  as  sucrose  and  dextrose 
during  ripening.  There  are  also  present  in  the  nitrogen-free 
extract  some  acids  or  acid  salts.  Certain  volatile  flavoring 
oils  are  included  in  the  crude  fat.  The  ash  of  fruits  is  very 
largely  basic  in  character  and  this  makes  fruit  very  valuable 
as  a  food.  Potash  is  an  important  constituent,  being  neces- 
sary for  the  ripening  process. 

98.  Stem  and  Leaf  Crops. — ^These  crops  when  green  are 
high  in  water  which  is  largely  eliminated  during  the  curing 
process  (Section  100).  The  dry  matter  of  these  crops  is 
high  in  ash  and  crude  fiber,  but  low  in  nitrogen-free  extract 
and  fat.  They  are  not  so  high  in  crude  fiber  as  the  straws  of 
the  grains,  partly  because  they  are  cut  before  so  much  of 
the  starch  and  other  digestible  carbohydrates  are  changed  to 
crude  fiber.    The  ash  is  rich  in  lime  and  potash,  but  not  much 


CROP  CHEMISTRY 


115 


silica  is  present.   The  changes  that  take  place  during  the  cur- 
ing process,  or  haymaking,  are  discussed  later  (Section  100). 


Fig.  27. — Fruit  crop:    Apples. 


99.  Vegetable  Crops. — ^These  crops,  like  the  fruits,  are 
very  high  in  water. 

(a)  Stem  Vegetables  as  a  class  are  the  highest  in  water 
content  of  all  the  crops,  over  94  per  cent.    Of  the  dry  matter, 


116 


CROPS 


nitrogen-free  extract  is  the  largest  in  amount,  although 
compared  to  the  grain  seeds  this  constituent  is  smaller; 
ash,  protein,  fiber,  and  fat  all  being  larger  in  amount.  It  is 
the  bases  in  the  ash  which  make  the  vegetables  an  important 
class  of  foods. 

(6)  Leaf  Vegetables  (Fig.  28). — These  do  not  differ  much 
in  composition  from  the  stem  vegetables.  Stems  and  leaves 
have  been  classed  together  in  the  other  crops. 


Fig.    28. — Leaf   vegetable   crop:      Cabbages.      Horticultural    Department, 
Pennsylvania  Station. 

(c)  Root  Vegetables  (Fig.  29). — Of  these  the  beets  are 
noted  for  their  sugar  content,  especially  the  sugar  beet  which 
runs  about  15  per  cent,  sucrose.  Potatoes  are  much  the 
highest  in  nitrogen-free  extract  of  any  of  the  vegetables,  and 
this  is  mostly  starch. 

(d)  Fruit  Vegetables. — As  would  be  expected  these  run 
lower  in  ash  than  the  other  vegetables,  although  on  a  dry 
basis  this  constituent  is  higher  than  it  is  in  grain  seeds. 
The  ash  is  largely  potash.    Crude  fiber  is  less,  fat  is  higher. 

100.  Hay. — Stem  and  leaf  crops,  or  fodder  crops  as  they 
are  customarily  called,  do  not  keep  well  unless  cured  or 
preserved  in  some  way.  One  of  the  common  methods  is  to 
make  hay  out  of  them.  The  usual  hay  crops  are  timothy  and 
clover,   although  many  other    grasses    and    legumes,  par- 


CROP  CHEMISTRY 


117 


ticularly  alfalfa  (Fig.  30),  are  grown  for  this  purpose.  What- 
ever the  crop,  the  principle  is  the  same,  namely,  to  cut  the 
crop  when  it  is  in  the  best  condition  for  making  a  valuable 
hay,  and  to  dry  it  or  cure  it. 


Fig.  29. — Root  vegetable  crop:    Potatoes. 

101.  Chemical  Changes  in  Making  Hay. — As  noted  in 
Table  I,  the  fodder  crops  range  in  moisture  content  from  60 
to  80  per  cent.,  whereas  hay  runs  from  8  to  15  per  cent., 
except  in  the  case  of  cured  corn  fodder  which   contains 


118 


CROPS 


42  per  cent,  of  water.  In  addition  to  a  mere  desiccation  of 
the  crop  there  are  changes  which  take  place  in  the  various 
constituents.     Table  IV  gives  the  changes  that  take  place 


Fig.  30. — Hay  crop:    Alfalfa.     Agronomy  Department,  Pennsylvania 

Station. 


Table  IV. 


Alfalfa: 

Green 

Hay    .      . 
Alsike  clover: 

Green 

Hay     .      . 
Corn  fodder: 

Green 

Cured 
Orchard  grass: 

Green 

Hay    .      . 
Red  clover: 

Green 

Hay     .      . 
Timothy: 

Green 

Hay    .      . 


-Changes  in  Composition  During  Haymaking 
(Calculated  to  Dry  Basis) 

Nitrogen- 
Crude  Crude  free  Crude 
Ash.             protein.            fiber.              extract.  fat. 


9.6 

17.0 

26.3 

43.6 

3.5 

8.1 

15.6 

27.3 

46.6 

2.4 

7.8 

15.3 

29.2 

44.0 

3.7 

9.3 

14.2 

28.4 

44.9 

3.2 

5.6 

8.8 

24.1 

58.9 

2.6 

4.7 

7.8 

24.7 

60.1 

2.8 

7.4 

9.6 

30.4 

49.3 

3.3 

6.7 

9.0 

36.0 

45.4 

2.9 

7.2 

15.3 

27.8 

45.8 

3.9 

7.3 

14.5 

29.1 

45.2 

3.9 

5.4 

8.0 

30.7 

52.8^ 

3.1 

5.1 

6.8 

33.5 

^H^^k 

k,    2.9 

CROP  CHEMISTRY  119 

during  the  making  of  hay  from  alfalfa,  alsike  and  red  clovers, 
orchard  grass  and  timothy,  and  in  the  curing  of  corn  fodder. 
The  figures  are  all  reduced  to  the  dry  basis  so  that  they  may 
be  compared.  It  is  to  be  noted  that  a  loss  occurs  uniformly 
in  the  crude  protein  content,  in  nearly  every  crop  in  ash 
and  crude  fat,  whereas  there  is  little  change  in  the  nitrogen- 
free  extract,  and  an  increase  in  the  crude  fiber  in  nearly 
every  instance. 

The  drying  of  the  crop  is  of  the  greatest  importance  in 
haymaking,  for  the  presence  of  large  quantities  of  water  will 
promote  the  activities  of  fermentative  bacteria,  that  is,  the 
hay  will  rot.  This  rotting  is  in  large  measure  an  oxidation 
process  caused  by  the  action  of  bacteria.  Moisture  is 
necessary  for  the  life  of  the  bacteria,  and  changes  take  place 
which  render  the  hay  unfit  for  use  as  food.  This  bacterial 
oxidation  sometimes  raises  the  temperature  considerably, 
occurring  when  the  stack  is  not  ventilated  sufficiently,  and 
the  heat  is  not  conducted  away.  Moreover,  too  moist  hay 
encourages  the  growth  of  molds  which  destroy  the  value  of 
a  hay  as  food. 

During  the  drying  process  some  changes  take  place, 
probably  of  an  enzyme  nature,  whereby  compounds  like 
volatile  oils  develop,  thus  giving  flavor  and  palatability 
to  the  hay.  This  process  undoubtedly  continues  to  some 
extent  in  the  mow  or  stack. 

The  time  of  cutting  hay  is  of  importance.  It  must  be 
remembered  that  the  stems  and  leaves  are  the  valuable 
portion.  They  should  be  harvested  when  they  contain  as 
much  valuable  digestible  constituents  as  possible,  and  yet 
give  as  great  a  yield  as  is  consistent  with  the  other  factors. 
In  the  later  stages  of  growth  the  proteins,  fats,  and  carbo- 
hydrates are  moved  to  the  seed.  The  stems  and  leaves 
are  exhausted  of  these  constituents  and  at  the  same 
time  are  provided  with  more  cell  wall  material  or  crude 
fiber.  The  seeds  of  grasses  and  of.  the  hay  legumes  are  very 
small  and  are  easily  shaken  off  when  dry.  In  this  way  there 
would  be  lost  the  most  valuable  part  of  the  food,  were  the 
hay  to  be  made  from  mature  crops. 
■    Again,  hi  such  crops  as  alfalfa  most  of  the  protein  is  in 


# 


120  CROPS 

the  leaves.  If  the  plant  matures  before  cutting,  the  leaves 
become  brittle  and  are  easily  knocked  off,  and  in  this  way 
protein  is  lost.  Also  as  a  plant  grows  older,  and  the  seeds 
form,  the  ash  elements  which  are  of  value  to  stock  are  gradu- 
ally lost  from  the  plant,  largely  by  being  exuded  on  the 
surface  of  the  leaves  and  washed  off  by  rains.  In  addition, 
the  older  a  fodder  crop  gets,  particularly  timothy,  the  less 
protein  and  fat,  and  the  more  crude  fiber  and  nitrogen-free 
extract  there  are  in  the  dry  material  (See  Table  V). 

Table  V. — Changes  in  the  Composition  of  Timothy  During 
Growth 

(Pounds  in  100  of  Dry  Matter) 


Before  bloom, 

Ash. 

Crude 
protein. 

Crude 
fiber. 

Nitrogen- 
free 
extract. 

Crude 
fat. 

headed 

7.7 

11.3 

26.3 

50.9 

3.8 

In  full  bloom     . 

5.7 

7.9 

29.9 

53.6 

2.9 

Just  after  bloom     . 

5.7 

7.1 

30.9 

53.2 

3.1 

In  seed,  nearly  ripe 

5.7 

6.6 

30.7 

54.2 

2.8 

If  cut  too  early,  on  the  other  hand,  the  crop  will  be  too 
small  and  not  a  maximum  amount  of  inorganic  material 
will  have  been  absorbed  by  the  plant.  In  fact  all  of  the 
constituents  will  be  small  in  amount.  Although  the  time 
of  cutting  hay  will  vary  with  the  crop  and  the  purpose  to 
which  it  is  to  be  put,  and  will  also  depend  somewhat  on 
weather  and  other  conditions,  the  proper  time,  in  general, 
to  cut  hay  crops  is  when  they  are  beginning  to  bloom. 
Later,  of  course,  a  larger  yield  will  be  obtained  but  the 
quality  will  not  be  as  good,  and  the  palatability  and  color 
will  not  be  as  desirable. 

The  proper  methods  of  curing  and  storing  hay  are  not 
to  be  considered  in  a  work  of  this  kind,  but  there  is  one 
practice  which  should  be  mentioned  here.  Some  farmers 
have  a  habit  of  mixing  salt  or  lime  with  the  hay  in  stacking, 
with  the  idea  of  preserving  it,  especially  if  it  has  been  neces- 
sary to  stack  the  hay  a  little  wetter  than  usual.  Salt  and 
lime  may  prevent  the  action  of  bacteria  and  fungi  to  some 
extent,  although  no  definite  information  is  available.  Cer- 
tainly stock  like  salted  hay,  but  that  is  on  account  of  the 


CROP  CHEMISTRY  121 

salt.  Lime,  on  the  other  hand,  does  not  improve  the  taste 
of  the  hay.  The  value  of  either  of  these  materials  as  a 
preservative  is  very  questionable. 

102.  Silage. — Inasmuch  as  haymaking  is  in  large  measure 
a  drying  process  the  resulting  material  is  dry,  and  for  general 
feeding  purposes  a  certain  amount  of  more  succulent  food 
is  desirable.  Silage  answers  this  purpose.  It  is  usually 
made  from  corn,  but  sometimes  mixtures  of  corn  and  cow- 
peas,  corn  and  soja  beans,  oats  and  vetch  are  employed. 
Those  crops  which  do  not  field  cure  or  dry  readily  are  best 
employed  for  silage.  Corn  is  particularly  well  adapted  for 
this  purpose  because  of  its  succulence  and  also  because  it  is 
an  economical  crop  to  use,  for  the  more  mature  it  becomes 
the  better  is  its  composition  from  a  feeding  point  of  view. 
Hay,  on  the  other  hand  (Section  101),  becomes  less  digestible, 
containing  less  ash,  protein,  and  fat,  and  more  crude  fiber. 
The  corn  crop  not  only  increases  in  weight  with  maturity, 
but  also  improves  in  quality,  containing  more  crude  fat 
and  nitrogen-free  extract,  much  less  crude  fiber,  and  not 
very  much  less  ash  and  crude  protein  (See  Table  VI).    The 

Table  VI. — Changes  in  the  Composition  of  Corn  During 
Growth 

(Pounds  in  100  of  Dry  Matter) 

Date  of  harvest. 
Aug.  15,  ears  beginning  to  form 
Aug.  28,  a  few  roasting  ears 
Sept.  4,  all  roasting  ears    . 
Sept.  12,  some  ears  glazing 
Sept.  21,  all  ears  glazed 

material  for  silage  is  cut  fine  and  packed  tightly  in  an  air- 
tight receptacle,  called  a  silo  (Figs.  31  and  74).  The  object 
is  to  keep  the  material  away  from  the  air  as  much  as  possible. 
Since  it  is  a  moist  material  the  presence  of  air  will  hasten 
bacterial  action  and  cause  putrefaction. 

103.  Chemical  Changes  in  Silage  Making. — Decomposition 
occurs  to  some  extent.  Some  of  the  sugars,  usually  dextrose 
in  corn,  are  fermented  by  yeasts  to  alcohol,  and  the  alcohol 
is  changed  by  acetic  bacteria  to  acetic  acid.    Lactic  bacteria 


Nitrogen- 

Crude 

Crude 

free 

Crude 

Ash. 

protein. 

fiber. 

extract. 

fat. 

9.31 

14.94 

26.47 

46.63 

2.65 

6.51 

11.71 

23.31 

55.49 

2.98 

6.19 

11.36 

19.69 

59.74 

3.02 

5.57 

9.58 

19.33 

62.59 

2.93 

5.92 

9.23 

18.59 

63.30 

2.96 

122 


CROPS 


convert  part  of  the  sugar  into  lactic  acid.  There  are  also 
small  amounts  of  butyric  and  some  other  acids  formed,  the 
total  acidity  amounting  to  not  more  than  2  per  cent,  nor 
usually  less  than  1  per  cent.  It  is  sometimes  stated  that  these 
acid  changes  are  due  not  to  bacteria  but  to  intermolecular 
respiration  in  the  plant  cells.  Whether  caused  by  bacteria 
or  intermolecular  respiration,  the  accumulation  of  acid 
stops  the  process,  thus  accounting  for  the  maxmium  of 
2  per  cent.  acid. 


Fig.  31.— Silos. 


In  addition  to  these  changes  there  is  also  a  loss  of  protein 
and  a  formation  of  amides,  possibly  due  to  enzyme  changes 
analogous  to  the  usual  hydrolytic  changes  of  protein  within 
the  plant.  Moreoever,  some  nitrogenous  material  decomposes 
to  ammonia,  which  forms  salts  with  the  acids  present.  Crude 
fiber  is  softened  and  made  more  digestible,  being  partly 
hydrolyzed  in  all  probability.  Other  compounds  in  the 
nature  of  volatile  oils  are  formed,  which  add  to  the  palata- 
bility  of  the  material.  There  is  also  a  complete  decomposition 
of  some  of  the  organic  material.  There  is  oxidation  to  carbon 
dioxide  and  water,  either  by  bacteria  or  oxidases,  resulting 
in  a  loss  of  dry  matter  amounting  to  10  or  15  per  cent. 


REFERENCES  123 


EXERCISES 

1.  Why  is  dried  material  extracted  in  a  crude  fat  determination?  Why 
is  alcohol-free  ether  used  in  this  determination?  What  substances  does  the 
ether  extract? 

2.  List  all  the  types  of  substances  that  are  found  in  plants.  In  which  of 
the  six  groups  of  the  Weende  method  does  each  fall? 

3.  Compare  the  analyses  of  seed  and  straw  of  barley  by  the  Weende 
method.  To  what  extent  are  these  figures  relatively  as  you  would  expect 
them  to  be  from  your  former  knowledge,  and  why?  Compare  wheat,  straw 
and  potatoes  in  the  same  way. 

4.  Would  a  crop  containing  more  crude  protein  than  nitrogen-free  extract 
be  a  better  crop  to  feed  for  energy  production  than  one  containing  more  of 
the  latter  than  of  the  former  and  why?  Substitute  crude  fiber  for  crude 
protein  in  the  alx»ve  question  and  then  answer  it. 

5.  Explain  why  calcium  and  potassium  are  so  necessary  for  alfalfa  and 
red  clover. 

6.  Given  a  rotation  of  corn,  oats  and  hay  (timothy  and  red  clover),  tell 
which  crops  would  remove  nitrogen  and  phosphorus  and  but  little  potassium, 
also  which  crops  would  remove  potassium  and  but  little  nitrogen  and 
phosphorus. 

7.  How  many  samples  must  be  weighed  out  in  order  to  make  a  Weende 
determination? 

8.  State  whether  plant  food  applied  to  the  following  crops  should  be  com 
paratively  high  in  N,  P2OS,  or  K2O:  Potatoes,  corn  and  strawberries. 
Consider  these  plant  foods  functionally  and  then  state  whether  or  not  the 
figures  found  are  what  you  would  expect  them  to  be.     (See  Table  111.) 

9.  State  why  or  why  not  you  would  expect  seeds  to  be  low  in  ash. 

10.  Cucumbers  contain  95.4  per  cent,  water.  Explain  why  they  are  not 
easily  crushed. 

1 1 .  Write  equations  for  the  chemical  changes  that  take  place  in  hay  mak- 
ing and  silage  production.  Why  cannot  equations  be  written  for  all  of  these 
changes? 

REFERENCES 

Conn.,  Storrs,  Agr.  Expt.  Sta.,  Bui.  70.     Silage  Fermentation. 

Farmers'  Bui.  No.  578,  U.  S.  Dept.  Agr.    Making  and  Feeding  of  Silage. 

Halligan.     Elementary  Treatise  on  Stock  Feeds  and  Feeding. 

Kans.  Bui.  155.     Alfalfa. 

Kans.  Bui.  175.     Grasses. 

Office  of  Experiment  Stations,  Appendix  Bui.  15,  U.  S.  Dept.  Agr.  Com- 
position of  Various  Crops. 

Office  of  Experiment  Stations,  Bui.  28,  U.  S.  Dept.  Agr.  Chemical  Com- 
position of  American  Food  Materials. 

Van  Slyke.     Fertilizers  and  Crops. 


PART  II 

FACTORS  IN  PLANT  GROWTH 


CHAPTER  V 

THE  AIR 

Of  all  the  factors  which  influence  plant  growth,  there  is 
one  over  which  the  farmer  has  no  control  and  yet  one  which 
is  absolutely  necessary  to  the  life  of  both  plants  and  animals. 
This  factor  is  the  air.  It  is  important  not  only  because  it 
supplies  plants  and  animals  with  certain  essential  elements, 
but  also  because  its  constituents  and  the  changes  in  these 
constituents  cause  variations  in  climate.  Moreover,  the  air 
and  its  constituents  have  a  very  considerable  effect  on  the 
formation  and  decomposition  of  soils.  It  is,  in  short,  of 
such  vital  importance  to  the  farmer  that  a  short  discussion 
of  its  properties  and  constituents  is  advisable  at  this  point, 

104.  Height  of  the  Air. — If  the  air  were  of  the  same 
density  throughout  it  would  extend  away  from  the  earth  for 
five  or  six  miles,  but  since  its  density  becomes  less  as  the 
distance  from  the  earth  increases,  it  has  been  estimated  that 
our  planet  is  enclosed  within  a  gaseous  envelope  about  200 
miles  thick. 

105.  Pressure  or  Weight  of  the  Air. — At  sea  level,  and 
at  0°  C.  the  air  exerts  normally  a  pressure  or  weight  of  1033 
grams  per  square  centimeter.  This  is  14.7  pounds  per 
square  inch  or  46,100  tons  per  acre.  The  pressure  diminishes 
with  the  altitude.  At  an  elevation  of  about  18,000  feet  the 
pressure  is  one-half  that  at  sea-level,  and  at  36,000  feet 
about  one-fourth.  Since  the  average  farm  is  not  at  sea- 
level  it  would  be  reasonable,  then,  to  say  that  the  weight  of 

(125) 


126  THE  AIR 

the  air  on  each  acre  is  in  round  numbers  45,000  tons.  The 
pressure  or  weight  of  the  air,  however,  is  never  constant;  it 
varies  from  day  to  day,  from  season  to  season,  and  from 
latitude  to  latitude.  It  is  lower,  for  example,  at  the  poles 
and  at  the  equator  than  it  is  between  these  two  latitudes. 

106.  Properties  of  the  Air. — ^The  air  is  usually  a  trans- 
parent, colorless,  odorless,  mechanical  mixture  of  gases, 
vapor,  and  solids,  the  latter  existing  in  exceedingly  fine 
particles.  1000  cc.  of  air  weigh  1.293  grams.  By  cooling 
and  pressure  it  can  be  condensed  to  a  bluish,  mobile  liquid, 
whose  boiling  point  is  about  — 195°  C.  Its  specific  gravity  is 
0.9.  There  exist  in  it  particles  of  ice  from  frozen  water,  and 
solid  carbon  dioxide.    These  can  be  removed  by  filtration. 

107.  Water  Vapor. — Ordinary  air  contains  varying 
amounts  of  water  vapor,  on  the  average  about  1.3  per  cent, 
by  volume  or  0.84  per  cent,  by  weight.  There  is  a  limit  to 
the  amount  of  water  vapor  that  the  air  will  retain.  When 
that  limit  is  reached  water  is  condensed  to  drops  and  we 
have  rain,  or  snow  if  it  is  cold  enough  to  freeze  the  drops. 
The  higher  the  temperature  the  more  water  vapor  can  be 
held  by  the  air.  For  instance,  at  0°  C,  1  cubic  meter  of 
air  will  hold  4.8  grams,  whereas  at  20°  C,  "ordinary  room 
temperature,"  1  cubic  meter  will  hold  17.1  grams.  When  the 
air  is  saturated  at  any  given  temperature,  a  lowering  in  the 
temperature  will  result  in  precipitation.  A  glass  of  ice  water 
"  sweats,"  that  is,  moisture  is  condensed  from  the  surrounding 
air  by  a  lowering  of  the  temperature  below  which  the  moisture 
can  be  retained.  That  temperature  at  which  air  begins  to 
deposit  water  is  called  the  dew  point  and,  of  course,  will 
vary  with  the  amount  of  water  vapor  present  in  the  air. 
Dew  is  deposited  at  night  when  objects  are  cooled  off  by 
radiation  to  such  an  extent  that  their  temperature  is  below 
the  dew  point  of  the  surrounding  air. 

108.  Temperature  of  the  Air. — The  presence  of  water 
vapor  in  the  air  modifies  the  temperature  to  a  very  great 
extent.  Perfectly  dry  air  absorbs  practically  no  heat  from 
the  sun's  rays.  They  pass  through  and  warm  up  the  earth. 
And  in  the  same  way  at  night,  heat  radiates  from  the  earth, 
passing  through  dry  air  with  but  little  absorption.    In  the 


COMPOSITION  OF  THE  AIR  127 

dry  regions  of  western  United  States,  the  days  are  very 
hot.  The  sun's  heat  rays  pass  through  the  air  unchecked. 
At  night,  on  the  other  hand,  it  is  very  cool,  because  the  heat 
has  radiated  away  again.  Water  vapor  and  particles  of 
dust  in  the  air  absorb  the  heat.  A  cloud  blanket  does  not 
permit  of  radiation  from  the  earth,  nor  does  it  permit  much 
heat  to  pass  through  to  the  earth.  On  a  cloudy  night  there 
is  not  so  much  danger  of  frost  as  on  a  clear  night,  since  the 
heat  is  not  radiated  off  into  space  so  rapidly. 

Air  is  warmed  by  contact  with  its  own  water  vapor,  or 
with  the  earth.  When  a  surface  of  water  is  evaporating 
heat  is  being  absorbed;  when  water  vapor  condenses  heat 
is  liberated.  The  specific  heat  of  water  is  1,  whereas  air 
is  only  0.240,  and  the  weight  of  a  given  volume  of  air  is  ^^ 
of  the  weight  of  an  equal  volume  of  water.  Thus  when  a 
large  body  of  water  warms  up  one  degree  and  evaporation 
takes  place,  a  volume  of  surrounding  air  equal  to  3200  times 
the  volume  of  the  body  of  water  is  cooled  down  one  degree. 
And,  conversely,  when  a  body  of  water  cools  down  one  degree, 
the  surrounding  air  to  the  extent  of  3200  times  the  volume 
of  water  is  warmed  up  one  degree.  This  accounts  for  the 
modifying  effect  of  large  bodies  of  water  on  the  climate  of 
nearby  land.  This  accounts,  also,  for  the  mild  climate  of 
western  Europe  which  is  washed  by  the  warm  Gulf  Stream. 

109.  Composition  of  the  Air. — The  constituents  of  the  air 
other  than  water  vapor,  which  is  exceedingly  variable,  are 
arranged  in  Table  VII  in  the  order  of  their  amounts : 

Table  VII. — Atmospheric  Constituents 

Per  cent.  Per  cent. 

Constituents.  by  volume.  by  weight. 

Nitrogen 78.03  75.51 

Oxygen  20.99  23.14 

Argon     . 0.94  1.29 

Carbon  dioxide 0.03  0  05 

Hydrogen 0.01  0.001 

Compounds  of  nitrogen     ....  Trace  Trace 

Bacteria "  " 

Dust,  etc "  " 

To  give  a  striking  illustration  of  the  different  amounts  of 
the  constituents  of  the  air,  a  slight  modification  of  Graham's 


128  THE  AIR 

suggestion  is  interesting.  If  the  air  is  imagined  to  be  sepa- 
rated into  its  several  parts  and  these  to  be  arranged  around 
the  earth  in  the  order  of  their  specific  gravities,  water  vapor 
being  condensed,  there  would  be  first  a  layer  of  water  five 
inches  thick,  then  thirteen  feet  of  carbon  dioxide,  next  ninety 
yards  of  argon,  then  a  mile  of  oxygen,  and  finally  four  miles  of 
nitrogen,  with  possibly  three  or  four  feet  of  hydrogen  on  top. 

(a)  Nitrogen. — ^The  amount  of  nitrogen  in  the  air  varies 
but  little.  It  is  the  most  constant  of  all  the  constituents. 
It  is  a  very  inert  gas,  uniting  with  other  elements  only  at 
high  temperatures.  It  acts  in  the  air  in  part  as  a  diluent, 
rendering  the  activity  of  oxygen  less  energetic.  It  is  the 
ultimate  source  of  all  nitrogenous  compounds.  The  means 
by  which  it  has  been  made  to  combine  with  other  elements 
is  bacterial  in  nature  (see  Section  125).  By  these  means 
it  is  removed  from  the  air,  but  is  returned  in  small  measure 
in  the  free  state  by  the  decomposition  of  nitrogenous  organic 
matter,  and  by  the  burning  of  all  kinds  of  fuel  or  other  or- 
ganic material  containing  nitrogen.  The  ordinary  com- 
bustion of  one  ton  of  coal  releases  from  one  to  five  pounds 
of  nitrogen. 

(6)  Oxygen. — This  constituent,  although  fairly  constant 
in  amount,  has  been  known  to  vary  from  20.53  per  cent,  by 
volume  to  21.03  per  cent.  Since  a  man  consumes  about 
600  liters  of  oxygen  in  a  day,  and  a  ton  of  coal  in  burning 
consumes  about  1,500,000  liters,  it  can  easily  be  seen  that 
the  air  of  cities,  which  are  densely  populated  and  where 
much  manufacturing  is  carried  on,  has  a  lower  percentage 
of  oxygen  than  the  open  country.  And  this  is  further  empha- 
sized by  the  fact  that  the  country  is  where  large  numbers  of 
growing  plants  are  to  be  found,  and  in  photosynthesis  oxygen 
is  given  off  by  plants.  Oxygen,  as  has  been  noted  in  Chapters 
II  and  III,  is  necessary  for  the  germination  of  the  seed  and  the 
growth  of  the  plant.  It  is,  moreover,  absolutely  necessary 
for  the  life  of  man  and  other  animals. 

(c)  Carbon  Dioxide. — Of  the  important  constituents  of 
the  air,  carbon  dioxide  is  the  smallest  in  amount  and  the  most 
variable,  with  the  exception  of  water  vapor.  Although 
normal,  pure  air  contains  about  0.03  per  cent,  by  volume, 


COMPOSITION  OF  THE  AIR  129 

city  air  contains  0.05  to  0.07  per  cent.>  and  the  carbon  dioxide 
in  the  air  of  crowded  auditoriums  may  rise  to  0.5  per  cent. 
At  night  the  amount  of  carbon  dioxide  is  greater  than  during 
the  day,  because  of  the  inactivity  of  plants  in  the  dark.  Since 
one  man  exhales  about  550  liters  of  carbon  dioxide  daily, 
and  a  ton  of  coal  gives  off  in  burning  about  1,500,000  liters 
of  carbon  dioxide,  it  is  easy  to  account  for  the  higher  pro- 
portion of  carbon  dioxide  in  the  air  of  cities.  In  the  country 
where  there  are  many  plants  and  a  large  area  of  leaf  surface 
absorbing  carbon  dioxide,  the  amount  is  naturally  less  (see 
Frontispiece).  An  acre  of  corn,  for  example,  at  the  height 
of  the  growing  season  would  absorb  about  10,000  liters  of 
carbon  dioxide  per  day,  and  it  has  been  estimated  that  an 
acre  of  forest  uses  up  about  6000  liters  per  day.  In  addition 
to  these  compensatory  changes  in  the  amount  of  carbon 
dioxide  in  the  air  there  are  volumes  poured  into  the  air  by 
some  volcanoes  and  other  openings  in  the  earth.  The 
decay  of  organic  matter  causes  evolution  of  carbon  dioxide; 
the  weathering  of  rocks  on  the  other  hand  uses  up  some 
carbon  dioxide  (Section  128),  The  amounts  of  carbon 
dioxide  absorbed  do  not  balance  the  amounts  given  off  into 
the  air.  The  ocean  apparently  acts  as  a  regulator  of  the 
amount.  When  there  is  any  increase  in  the  percentage  of 
carbon  dioxide  in  the  air  this  naturally  increases  the  pressure 
of  carbon  dioxide  on  the  surface  of  the  water  and  some  is 
dissolved  and  changed  to  bicarbonate  of  calcium.  On  the 
other  hand  a  diminution  in  the  amount  causes  a  lowering 
in  the  pressure  and  some  bicarbonate  of  calcium  changes  to 
carbonate  again  and  releases  carbon  dioxide.  In  this  way 
there  is  maintained  a  fairly  uniform  amount  of  carbon 
dioxide  in  the  air. 

{d)  Argon  and  Hydrogen. — ^Argon  is  one  of  the  so-called 
rare  elements.  It  has  no  agricultural  bearing,  and  is  so 
inert  that  it  will  unite  with  no  other  element.  In  fact  its 
name  means  that  it  will  not  work.  In  addition  there  are 
several  other  rare  gases  existing  in  much  smaller  amounts, 
but  none  of  them  is  of  any  importance.  Hydrogen,  also, 
although  present  in  the  air  in  fairly  constant  quantities, 
is  of  no  agricultural  value  and  need  not  be  considered. 
9 


130  THE  AIR 

(e)  Compounds  of  Nitrogen. — ^These  compounds  are  of 
importance  as  far  as  they  go,  but  the  amount  present  is  very 
small.  They  are  principally  oxides  of  nitrogen  and  am- 
monia, occurring  usually,  perhaps,  as  nitrous  and  nitric 
acids  and  ammonium  nitrite,  nitrate,  carbonate,  or  sulphate. 
The  oxides  of  nitrogen  are  formed  from  oxygen  and  nitrogen 
by  lightning  discharges.  The  intense  heat  in  the  immediate 
vicinity  of  the  electric  spark  causes  a  very  small  part  of 
these  gases  to  unite.  Ammonia  is  formed  by  the  decomposi- 
tion of  organic  matter,  although  free  nitrogen  is  formed 
under  some  conditions  (Section  124).  These  compounds  of 
nitrogen  can  be  used  very  well  by  plants  after  some  changes 
in  the  soil,  but  the  amount  is  hardly  worth  considering 
ordinarily.  On  the  average  there  are  about  three  pounds  of 
nitrogen  brought  to  the  surface  of  an  acre  in  a  year  by  rain 
and  snow.  Occasionally  this  may  amount  to  ten  pounds, 
but  very  rarely. 

(/)  Bacteria,— The  solid  particles  of  the  air,  besides  the 
nitrate,  carbonate,  and  sulphate  of  ammonium  mentioned 
above,  consist  of  bacteria  and  dust.  Bacteria  exist  in  count- 
less numbers  in  the  air,  invisible,  but  nevertheless  of  great 
importance,  sometimes  beneficial,  sometimes  harmful.  The 
bacteria  which  aid  in  decomposing  organic  matter  in  the 
soil  and  in  making  nitrogen  available  are  all  carried  in  the 
air  and  help  the  farmer  very  materially.  Moreover,  the 
germs  of  many  diseases  are  carried  through  the  air  and  work 
considerable  harm.  One  proof  of  the  presence  of  bacteria  in 
the  air  is  to  be  found  in  the  fact  that  if  perfectly  sterile  milk 
is  exposed  to  the  air  for  any  length  of  time  it  will  sour,  due 
to  the  lactic  acid  bacteria  being  carried  to  it  by  the  air. 

(g)  Dust, — Fine  particles  of  dust  are  everywhere  present 
in  the  air,  and  consist  of  minute  particles  of  organic  matter, 
bits  of  cotton,  pieces  of  hair,  and  fragments  of  minerals. 
There  may  also  be  pollen  from  flowers,  and  spores  of  fungi. 
These  particles  of  dust  form  nuclei  for  the  precipitation  of 
water  vapor  and  hence  cause  the  formation  of  fog  and  clouds. 
Dustless  air  would  contain  no  fog. 

(h)  Sulphur  Dioxide  is  of  very  serious  consequence  in 
some  places.    In  the  western  part  of  the  United  States  where 


REFERENCES  131 

smelters  have  been  erected  for  the  treatment  of  sulphide 
ores,  large  volumes  of  sulphur  dioxide  are  discharged  into 
the  air  during  the  roasting  of  the  sulphides.  This  has  a 
very  harmful  effect  on  vegetation  and  has  led  to  legislative 
action  in  a  number  of  states.  Not  only  does  the  gas  itself 
harm  vegetation,  but  its  solution  in  rain  water  as  sulphurous 
acid  is  poisonous.  In  large  cities  where  much  soft  coal  is 
burned  sulphur  dioxide  is  present  in  the  air  and  this  accounts 
in  part  for  the  weak,  sickly  appearance  of  trees  and  grass 
in  such  centers  of  industry. 

EXERCISES 

1.  List  the  components  of  air.  State  the  processes  by  which  each  com- 
poneht  serves  in  a  beneficial  or  harmful  way  to  agriculture,  and  how. 

2.  Explain  why  the  temperature  on  the  shores  of  the  Great  Lakes  is 
more  constant  than  150  miles  inland. 

3.  1,8  moist  or  dry  air  the  heavier?  Why?  What  instrument  in  common 
use  can  detect  the  difference? 

4.  Why  is  the  farmer  more  uncomfortable  while  making  hay  on  a  moist 
day  than  on  a  dry  day  of  the  same  temperature? 

5.  Why  are  thunderstorms  of  any  value  to  agriculture? 

6.  Frond  what  sources  are  the  principal  components  of  the  air  continually 
derived?  By  what  means  are  they  removed?  Why  is  the  composition  of 
the  air  so  nearly  constant  all  over  the  earth? 

7.  What  would  be  the  result  of  making  your  animals  work  in  an  atmos- 
phere whose  nitrogen  content  was  materially  lessened? 

8.  Why  is  the  farmer's  wife  at  preserving  time  so  very  careful  not  to  get 
any  unheated  air  into  her  preserves? 

9.  Why  will  freshly  drawn  milk  spoil  more  quickly  when  kept  exposed  to 
the  atmosphere  than  when  kept  in  sealed  containers? 


REFERENCES 

McPherson  and  Henderson.     General  Chemistry. 

Newth.     Inorganic  Chemistry. 

Smith.     General  Chemistry  for  Colleges. 

Any  other  good  text-book  on  general  chemistry. 


CHAPTER  VI 

THE  SOIL:  ORGANIC  MATTER 

That  portion  of  the  earth's  crust  which  can  support 
vegetation,  or  can  raise  crops,  is  what  the  farmer  terms  the 
soil.  That  loose  mass  of  particles  derived  from  rock  dis- 
integration and  decay,  and  which  covers  most  of  the  land 
portion  of  the  globe  is  the  way  the  geologist  defines  the  soil. 
These  definitions  for  the  most  part  describe  the  same  mate- 
rial but  geological  soil  is  not  always  agricultural  soil,  for 
not  all  loose  rock  particles  will  raise  crops,  and  hence  to  the 
farmer  are  not  soil. 

110.  Ck>inposition  of  Soil. — Soil  agriculturally  is  composed 
of  fine  and  coarse  particles  of  rock  in  all  stages  of  decompo- 
sition, of  organic  matter  derived  from  decayed  or  decaying 
plants  and  animals,  of  water,  of  bacteria,  fungi,  and  other 
forms  of  life,  and  of  gases. 

111.  Function  of  the  Soil. — Soil  serves  not  only  as  an 
anchorage  for  plants,  where  they  can  spread  out  their  roots 
and  maintain  a  position  which  will  enable  them  to  absorb 
the  sun's  rays  to  the  best  advantage,  but  also  serves  as  the 
source  of  most  of  those  elements  which  are  essential  to  the 
plant's  growth.  A  perfect  soil  is  one  which  maintains  a 
reserve  supply  of  insoluble  food  material  that  cannot  be 
washed  away;  which  produces  enough  soluble  material  to 
feed  the  growing  crop;  which  is  so  constructed  that  it  can 
supply  sufficient  water  to  the  crop;  which  is  capable  of  main- 
taining the  right  temperature  or  of  warming  up  quickly  in 
the  spring;  and  which  has  a  structure  that  permits  of  proper 
root  movement. 

112.  Soil  Study. — The  study  of  the  movements  of  water 
in  the  soil,  of  its  holding  capacity  for  water,  of  the  arrange- 
ment of  soil  clusters,  of  the  size  of  ultimate  particles,  of  the 
relations  of  soils  to  heat,  and  of  the  various  methods  of 

(132) 


ORGANIC  MATTER  133 

working  the  soil,  are  all  important  factors  for  the  farmer  to 
consider,  but  do  not  come  within  the  scope  of  agricultural 
chemistry.  The  study  of  the  important  compounds  in  the 
soil  and  the  changes  which  take  place  in  them;  in  other 
words  the  chemical  reactions  and  their  causes,  which  directly 
or  indirectly  affect  the  growth  of  crops,  do,  however,  com- 
prise soil  chemistry.  The  food  of  plants,  from  what  derived, 
how  made  soluble,  how  retained  in  the  soil  or  made  insoluble, 
are  particular  points  to  be  considered. 

Plant  food  is  derived  from  the  rock  particles  and  from  the 
organic  matter.  Soil  moisture,  organic  matter,  bacteria, 
fungi,  and  gases  are  factors  influencing  the  changes  taking 
place  in  plant  food.  The  mineral  particles,  and  the  organic 
matter  to  a  small  extent,  supply  the  compounds  containing 
phosphorus,  potassium,  sulphur,  calcium,  magnesium,  and 
iron.  The  organic  matter  is  the  source  of  nitrogen.  In 
taking  up  the  subject  of  plant  food  in  soils  it  seems  best 
to  discuss  first  the  organic  matter  which  has  been  very 
truthfully  called  the  life  of  the  soil.  It  is  probably  the  most 
important  single  factor  in  making  plant  food  soluble,  except 
of  course  water,  the  solvent  medium  itself. 

113.  Organic  Matter. — The  soil  is  separated  horizontally 
into  two  portions  as  it  lies  in  the  field :  First,  the  surface 
soil,  or  sometimes  called  merely  soil,  and  second,  subsoil. 
For  certain  purposes,  such  as  the  scientific  study  of  soils 
in  comparing  types,  it  is  advisable  to  arbitrarily  assume  that 
the  surface  six,  eight,  or  ten  inches  shall  be  the  surface  soil, 
and  all  below  that  shall  be  the  subsoil,  but  the  natural 
division  lies  at  the  place  where  the  color  of  the  soil  changes, 
frequently  very  abruptly,  almost  always  very  distinctly, 
from  dark  to  light  (Fig.  32).  This  depth  varies  in  different 
soils,  sometimes  lying  only  a  few  inches  below  the  surface 
of  the  land,  sometimes  lying  several  feet  below. 

It  is  in  this  dark  soil  that  crops  can  grow  best.  It  frequently 
happens  that  when  a  light  colored  subsoil  is  turned  up, 
crops  will  not  grow.  This  may  be  due  to  several  causes,  but 
one  of  them  at  least  is  the  absence  of  organic  matter  which 
gives  the  dark  color  to  surface  soil.  Organic  matter  in  the 
soil  is  composed  of  particles  of  roots,  leaves,  bark  and  other 


134 


THE  SOIL:  ORGANIC  MATTER 


plant  debris,  and  fragments  of  animals,  insects,  and  worms, 
in  all  stages  of  decomposition,  ranging  from  their  original 
condition  and  easily  recognizable,  down  to  the  unrecognizable 
pieces  and  the  amorphous,  waxy  coating  on  soil  grains.  The 
whole  mass  of  soil  material,  which  at  one  time  or  another  was 
a  part  of  living  organisms,  is  called  organic  matter.  Organic 
matter  in  the  process  of  decomposition,  which  is  changing 
continually  and  breaking  down  into  new  compounds,  may 
be  called  active  organic  matter.     That  particular  part  of  it 


Fig.  32. — Soil  and  subsoil,  showing  dark  color  due  to  organic  matter.    (Weir.) 


which  is  much  more  decomposed,  which  has  lost  all  resem- 
blance to  living  matter,  and  which  is  indistinguishable  among 
the  soil  grains,  except  that  it  gives  the  dark  color  to  them, 
may  be  called  inactive  organic  matter  or  humus. 

114.  Bacteria. — As  soon  as  a  portion  of  a  living  organism 
dies,  whether  it  be  a  leaf,  or  bit  of  bark,  or*  mass  of  roots,  it 
is  at  once  attacked  by  bacteria  which  are  everywhere  present 
in  the  soil.  Inasmuch  as  bacteria  are  of  such  vital  impor- 
tance to  agriculture,  both  beneficially  and  otherwise,  a  brief 
description  of  them  is  desirable. 


BACTERIA  136 

Bacteria  are  one-celled  plants  which  are  composed  of 
cell  walls  of  protein — not  cellulose — cell  contents  or  proto- 
plasm and  enzymes,  but  no  nucleus.  They  are  very  much 
like  any  of  the  simple  cells  in  crop  plants  except  for  the 
absence  of  nuclei.  These  bacterial  cells  require  soluble 
material  which  can  diffuse  through  their  walls  and  from  which 
can  be  built  up  the  various  components  of  the  cell  wall  and 
contents.  They  are  thus  permitted  to  reproduce  themselves 
by  subdivision.  The  cells  are  small,  about  1  micron  (0.001 
mm.)  in  diameter,  or  even  smaller.  Some  bacteria  are  more 
or  less  spherical,  others  are  rod-shaped,  perhaps  two  or  three 
times  as  long  as  they  are  wide,  and  some  of  them  are  spiral- 
shaped.  They  consist  of  about  85  per  cent,  of  water,  and 
of  the  dry  matter  some  8  per  cent,  is  composed  of  inorganic 
compounds.  The  rest  is  fat,  carbohydrate,  and  protein 
material  largely,  very  much  like  the  cell  contents  of  any 
plant. 

Bacteria  contain  no  chlorophyl,  hence  do  not  make  their 
organic  food  by  means  of  the  energy  derived  from  the  sun's 
rays.  The  energy  they  use  in  synthesizing  compounds  is 
derived  by  oxidation  of  various  compounds,  with  or  without 
the  aid  of  free  oxygen,  or  by  intermolecular  decomposition, 
which  releases  energy.  Many  bacteria,  like  crop  plants, 
oxidize  organic  compounds  to  carbon  dioxide  and  water. 
Some  oxidize  nitrogen,  sulphur,  iron,  and  other  inorganic 
elements  (considering  nitrogen  an  inorganic  element)  to 
nitrites  and  nitrates,  sulphuric  acid,  and  ferric  oxide.  In 
this  way  they  derive  energy.  Others  reduce  highly  oxidized 
compounds  like  nitrates  and  sulphates,  using  the  oxygen 
thus  derived  to  oxidize  other  compounds.  And  still  others 
merely  decompose  compounds  without  any  oxidation,  deriv- 
ing such  energy,  for  example,  as  is  released  when  dextrose  is 
changed  to  lactic  acid. . 

The  material  which  bacteria  use  as  food  for  tissue-forming 
purposes  is  largely  organic  in  nature,  although  there  are  some 
bacteria  which  live  without  any  organic  matter — that  is, 
they  use  inorganic  compounds  entirely  from  which  to  make 
their  cell  substance.  The  organic  material  that  is  most 
frequently  used  is  composed  of  the  various  carbohydrates, 


136  THE  SOIL:  ORGANIC  MATTER 

fats,  and  proteins  of  animal  and  plant  origin.  Those 
compounds  which  are  insoluble  are  rendered  soluble  by  the 
excretion  of  enzymes  which  acts  hydrolytically  usually,  to 
dissolve  the  compound.  The  soluble  substance  then  diffuses 
into  the  bacterial  cell  where  further  transformations  take  place. 

Since  enzymes  act  independently  of  the  living  cell  which 
produces  them,  they  frequently  form  sufficient  material  to 
kill,  or  at  least  to  stop  the  activities  of  the  bacteria  as  well 
as  of  themselves.  This  is  true  of  acid-  and  alcohol-forming 
enzymes  in  particular.  If  the  acid  can  be  neutralized  as 
fast  as  it  is  formed,  or  if  the  alcohol  is  further  changed, 
the  production  of  acid  and  alcohol  will  not  cease. 

Some  bacteria  use  oxygen,  while  some  do  not.  This  fact 
goes  one  step  further  in  that  many  of  the  oxygen-using,  or 
aerobic  bacteria,  can  not  live  at  all  in  the  absence  of  oxygen 
or  air,  and  in  that  many  of  those  which  do  not  use  oxygen,  or 
anaerobic  bacteria,  cannot  live  in  the  presence  of  free  oxygen 
or  air. 

115.  Decomposition  of  Organic  Matter. — In  the  soil,  as 
was  stated  above,  are  very  many  bacteria  of  all  kinds. 
Furthermore,  the  conditions  under  which  they  live  are  very 
different,  depending  on  the  physical  condition  of  the  soil 
and  on  the  kind  of  organic  matter  from  which  they  derive 
nourishment.  The  principal  difference,  however,  is  the 
presence  or  absence  of  air.  In  a  soil  that  is  fairly  open  and 
aerated  there  are  different  products  formed  from  those  in  a 
water-logged  or  non-aerated  soil.  It  is  not  easy,  however, 
to  classify  organic  decomposition  on  this  basis,  for  soils 
vary  gradually  all  the  way  from  those  containing  no  air  at 
all,  like  swampy  lands  under  water,  to  those  which  are  very 
thoroughly  penetrated  by  the  air,  like  loose,  sandy  lands. 

In  a  general  way  the  products  of  decomposition  can 
be  classified  into  two  groups:  First,  those  developed  under 
aerobic  conditions;  and  second,  those  developed  under 
anaerobic  conditions.  Under  aerobic  conditions  there  will 
be  produced  large  quantities  of  carbon  dioxide  and  water, 
mineral  salts  (set  free  by  oxidation  of  organic  matter  con- 
taining inorganic  elements),  and  nitrates,  but  not  much 
humus   (Section  117).     Under  anaerobic  conditions  there 


FACTORS  AFFECTING  RATE  OF  DECOMPOSITION     137 

will  be  produced  small  amounts  of  carbon  dioxide  and  water, 
considerable  humus,  and  in  addition  methane  and  hydrogen 
sulphide.  In  both  cases  there  will  be  varying  amounts  of 
organic  acids,  alcohols,  higher  hydrocarbons,  waxes,  etc. 

The  classification  holds  only  in  a  general  way.  Of  course, 
where  there  is  an  excess  of  air,  organic  matter  is  largely 
oxidized  to  carbon  dioxide,  water,  residual  inorganic  salts, 
and  nitrates.  As  the  amount  of  air  available  to  the  bacteria 
becomes  less,  oxidation  to  carbon  dioxide,  water,  nitrates, 
and  mineral  salts,  materially  lessens.  More  acids  and  alcohols 
form,  as  well  as  more  of  that  black,  amorphous  product 
called  humus.  As  the  air  supply  continues  to  decrease,  less 
and  less  carbon  dioxide  and  water  are  produced,  although 
their  formation  never  ceases  entirely,  for  intermolecular 
oxidation  sets  free  small  quantities.  The  production  of 
nitrates  practically  ceases  in  the  absence  of  air,  and  products 
that  result  from  reduction,  like  methane  and  hydrogen 
sulphide,  begin  to  form.  The  reduction  of  one  compound  is 
accompanied  by  a  simultaneous  oxidation  of  another  com- 
pound and  the  production  of  energy.  Considerably  more 
acids,  alcohols,  and  waxes  are  formed,  since  intermolecular 
decomposition  results  in  the  formation  of  these  compounds 
rather  than  of  the  completely  oxidized  forms.  At  the 
same  time  there  is  produced  more  and  more  of  this  curious, 
amorphous  mixture  called  humus.  In  soils  which  are 
absolutely  anaerobic,  however,  little  humus  is  formed.  In 
fact  under  conditions  where  no  air  at  all  is  present  decom- 
position is  very  slow.  Organic  matter  is  maintained  in  a 
fairly  well  preserved  condition.  In  peat  bogs,  for  example, 
the  structure  of  the  original  plants,  sphagnum  moss  in  many 
cases,  is  not  destroyed. 

The  bacteria  exist  in  soils  for  the  most  part  in  the  upper 
eight  to  ten  inches,  just  under  the  surface.  There  are  very 
few  on  top  of  the  ground,  for  direct  sunlight  kills  most 
bacteria. 

116.  Factors  Affecting  the  Rate  of  Decomposition. — The 
extent  to  which  decomposition  of  organic  matter  will  take 
place  theoretically  agrees  with  the  above  classification,  but 
the  amount  or  rate  of  decomposition  depends  on  two  prin- 


138  THE  SOIL:  ORGANIC  MATTER 

cipal  factors:  First,  the  number  of  bacteria  present;  and 
second,  the  kind  of  Uving  matter  undergoing  decomposition. 

(a)  Number  of  Bacteria  in  Soils, — As  to  the  number 
of  bacteria  in  soils,  it  will  vary  between  very  wide  limits. 
When  "number  of  bacteria"  is  mentioned  it  means  the 
number  of  colonies  of  bacteria  that  can  be  cultivated  from 
a  given  amount  of  soil  in  an  artificial  nutrient  solution  and 
subsequently  counted.  The  supposition  is  that  each  colony 
is  developed  from  a  single  bacterium.  The  numbers  vary 
from  100,000  to  50,000,000  or  even  100,000,000  per  gram 
of  soil.  The  average  cultivated  land  probably  contains 
several  million  per  gram.  The  more  bacteria  present,  the 
more  decomposition  takes  place  and  hence  a  greater  pro- 
duction of  those  various  compounds  mentioned  above, 
namely,  carbon  dioxide,  water,  mineral  salts,  and  nitrogenous 
compounds,  but  ordinarily  less  humus. 

The  number  of  bacteria  is  dependent  on  several  factors, 
the  principal  ones  being:  Temperature,  moisture,  food,  and 
reaction  of  the  soil,  whether  acid  or  alkaline. 

(1)  Temperature. — Bacteria  thrive  best  between  15°  and 
25°  C,  although  they  do  live  from  about  0°  to  40°  C.  Near 
0°  bacterial  life  is  inactive  although  not  dead.  Above  40° 
the  bacteria  begin  to  die;  at  100°  C.  most  bacteria  are  killed, 
although  the  spores  are  not. 

(2)  Moisture. — It  is  claimed  that  the  best  moisture  con- 
ditions for  bacteria  vary  from  8  to  10  per  cent,  in  sandy 
soils  to  20  per  cent,  and  even  more  in  heavy  clays.  As 
soils  dry  out  the  bacteria  for  the  most  part  merely  become 
dormant,  although  some  are  killed  outright.  Excessive 
water  tends  to  kill  off  the  aerobic  bacteria  but  encourages 
the  growth  of  the  anaerobes.  Since  for  the  most  part  the 
beneficial  bacteria  are  aerobes,  aeration  is  essential  to 
optimum  soil  conditions. 

(3)  Food. — ^This  includes  of  course  organic  matter  from 
which  most  bacteria  derive  their  sustenance.  Being  plants, 
they  must  have  inorganic  salts  as  well,  and  there  are  neces- 
sary such  salts  as  sulphates,  phosphates,  lime,  and  potash 
compounds,  derived  either  from  the  organic  remains  or  from 
mineral  particles  in  the  soil. 


HUMUS  139 

(4)  Reaction  of  the  Soil. — Most  beneficial  bacteria  require 
for  their  optimum  growth  a  neutral  or  alkaline  medium  in 
which  to  work.  The  presence  of  an  acid  inhibits  their 
growth  to  a  certain  extent.  Some  bacteria  produce  mineral 
or  organic  acids  as  a  result  of  their  own  activities,  and  these 
acids  after  reaching  certain  concentrations  not  only  check 
the  growth  of  the  bacteria  which  produce  them,  but  that  of 
other  bacteria  as  well.  If  there  are  sufficient  acid-neutral- 
izing compounds  in  the  soil,  such  as  calcium  carbonates, 
these  acids  are  neutralized  as  fast  as  formed  and  bacterial 
life  is  not  suspended. 

(6)  Kinds  of  Living  Matter. — ^Although  all  portions  of 
vegetable  and  animal  remains  are  attacked  by  one  kind  of 
bacteria  or  another,  and  eventually  can  be  entirely  decom- 
posed under  ordinary  soil  conditions,  some  parts  of  these 
remains  resist  decay  more  strongly  than  others.  This  is  due 
ordinarily  to  the  few  species  of  bacteria  which  can  attack 
these  parts  of  the  plant  or  animal  body. 

Cellulose  and  lignin — that  is,  the  hard,  woody  portion  of 
plants — resist  decay  more  strongly  than  the  softer,  more 
succulent  portions.  Large  roots,  bits  of  bark,  particularly 
bark  containing  tannins,  and  wood  in  general,  are  more 
resistant  than  leaves,  soft  stems,  and  fine  roots  like  those  of 
grass.  As  a  rule  fats  and  waxes  are  less  easily  decomposed 
than  sugars  and  most  of  the  proteins.  In  forests,  however, 
logs  and  stumps  gradually  decay  and  disappear  entirely, 
but  here  the  conditions  for  one  thing  are  most  favorable 
for  rapid  oxidation,  and  those  bacteria  and  fungi  which  are 
the  most  active  oxidizers  thrive. 

Most  animal  remains  decay  rapidly,  but  such  things  as  the 
organic  matter  in  bones,  hair,  or  hide  decompose  very 
slowly. 

117.  Humus. — The  accompaniment  of  almost  all  kinds 
of  organic  decomposition  in  soils  is  the  production  of  a  black 
or  dark  amorphous  material  which  is  called  humus.  It  is 
one  of  the  products  of  decay,  formed  for  the  most  part 
where  there  is  insuflBcient  oxygen  to  allow  complete  destruc- 
tion to  carbon  dioxide  and  water.  From  the  original  source, 
whether  it  be  root  or  leaf  or  stalk  or  animal,  the  humus  is 


140  THE  SOIL:  ORGANIC  MATTER 

distributed  among  the  soil  grains  with  considerable  uni- 
formity within  certain  limits.  That  is,  it  does  not  ordinarily 
extend  to  any  great  depth,  nor  does  it  extend  laterally 
over  a  field  with  uniformity,  owing  to  changing  conditions 
in  soil  masses,  but  the  grains  themselves  are  fairly  well 
covered  with  the  humus.  It  must  therefore  have  been  more 
or  less  soluble  in  water,  or  in  liquid  form  at  one  time  or 
another  at  least,  to  surround  the  particles.  Its  distribution, 
moreover,  is  aided  by  the  growth  and  final  decay  of  the  hyphse 
or  root-like  hairs  of  certain  fungi  which  feed  on  a  decaying 
bit  of  organic  matter.  It  is  no  uncommon  occurrence  to 
note  the  wide  ring  of  darker  soil  surrounding  a  decaying 
root.  Earthworms  also  distribute  humus  throughout  the 
soil  to  a  very  great  extent  by  passing  soil  through  their  bodies 
and  drawing  after  themselves  into  their  burrows  particles 
of  leaves  and  blades  of  grass.  In  some  localities  where 
earthworms  are  fairly  numerous,  Darwin  has  estimated 
that  they  work  over  in  a  year  from  0.1  to  0.2  of  an  inch 
of  surface  soil.  Ants,  burrowing  insects,  and  animals,  all 
help  to  distribute  organic  matter  and,  subsequently,  humus 
throughout  the  soil. 

118.  Properties  of  Humus. — If  a  dark  soil  containing 
considerable  humus  be  first  treated  with  a  dilute  mineral 
acid  like  hydrochloric,  and  then  with  ammonia,  a  black 
liquid  will  be  obtained.  The  soil  residue  after  washing  is 
very  much  lighter  in  color,  almost  white  in  some  cases. 
By  this  means  the  humus  has  been  dissolved  from  the  soil 
grains,  although  in  many  cases  it  may  not  be  of  exactly  the 
same  composition  as  it  was  in  the  soil.  If  the  water  is 
evaporated  from  this  solution  there  remains  a  shiny  black 
material,  rather  hard  and  scaly,  and  absorptive  of  water. 
If  it  is  burned  there  remains  behind  an  ash  of  inorganic 
material. 

Chemically,  humus  is  by  no  means  a  single  compound. 
It  is  a  mixture,  probably  a  mechanical  mixture,  of  many 
substances.  Research  by  the  Bureau  of  Soils  has  shown  that 
it  is  composed  of  acids,  carbohydrates,  fats,  waxes,  hydro- 
carbons, resins,  nitrogenous  compounds  of  various  kinds, 
black  compounds  or  pigments,  and  undoubtedly  many  com- 


ACID  HUMUS  141 

pounds  other  than  these  few  classes  mentioned.  Notwith- 
standing this  great  complexity,  the  black  material  has,  or 
perhaps  more  correctly,  these  numerous  compounds  colored 
black  have  certain  general  properties  which  afford  sufficient 
excuse  for  the  term  humus,  and  to  consider  them  as  a  single 
kind  of  material  in  the  soil. 

Using  the  term  "humus,"  then,  in  this  general  and  popular 
sense,  it  can  be  said  that  it  is  composed  of  the  same  elements 
as  are  plants,  except  that  there  is  more  carbon  and  nitrogen, 
and  less  oxygen,  hydrogen,  and  ash,  or  inorganic  material. 
Table  VIII  gives  the  percentage  composition  of  cellulose, 
grass,  oak  wood,  decayed  oak  wood,  and  humus,  showing  the 
changes  in  composition  from  fresh  material  to  humus. 

Table  VIII. — Composition  of  Humus  and  Humus-formino 


Materials 
Cellulose.  ,       Grass. 

Oak  Wood. 

Decayed 
Oak  Wood. 

Humus. 

44.2             50.3 

50.6 

56.2 

54.5 

6.3               5.5 

6.0 

4.9 

3.5 

49.5             42.31 

f41.5 

Carbon  . 
Hydrogen 
Oxygen 

\  43.4  38.9  -1 

Nitrogen      l.sj  [  0.5 

Results  on  the  ash  of  humus  are  not  of  sufficient  number 
for  any  definite  statement  to  be  made,  but  it  can  be  said  that 
whereas  plants  on  the  whole  contain  6.5  per  cent,  ash  (Section 
53),  humus  probably  does  not  contain  more  than  2  per  cent, 
on  the  average.  On  the  whole  humus  is  insoluble  in  water 
and  organic  solvents. 

Humus  can  be  divided  into  two  kinds  in  the  soil:  Acid 
humus,  and  neutral  humus,  both  with  the  same  physical 
properties. 

119.  Acid  Humus. — ^Acid  humus  is  formed  in  soils  lacking 
sufficient  neutralizing  materials.  It  is  insoluble  in  water,  acids, 
and  organic  solvents.  It  combines  with  bases  to  form  salts, 
particularly  those  of  the  alkaline  earths,  which  are  insolu- 
ble in  water,  and  of  the  alkalies,  which  are  soluble  in  water. 
By  treating  a  soil  containing  acid  humus — and  for  practical 
purposes  this  means  an  acid  soil — with  ammonium  hydroxide 
the  acid  humus  reacts  with  the  ammonium  hydroxide,  the  re- 


142  THE  SOIL:  ORGANIC  MATTER 

suiting  material  dissolving  in  the  solution  present,  A  dark 
or  black  liquid  results.  For  the  sake  of  convenience  in  dis- 
cussing humus  we  can  call  the  acid  humus,  humic  acid, 
remembering,  however,  that  it  is  not  a  single  acid  by  any 
means  but  a  mixture  which  acts  like  an  acid.  The  material 
combined  with  ammonium  hydroxide  would  then  be  called 
ammonium  humate.  Sodium  and  potassium  hydroxides 
react  like  ammonium  hydroxide.  From  a  solution  of  alka- 
line humate  a  mineral  acid  like  hydrochloric  precipitates 
humic  acid  which  separates  out  in  black  or  brown  flocks, 
drying  to  shiny  scales. 

120.  Neutral  Humus. — ^Where  the  soil  contains  sufficient 
calcium  or  other  carbonate,  humic  acid  is  neutralized  as 
fast  as  it  is  formed  and  the  humus  may  then  be  said  to  be 
calcium  (or  other  basic  element)  humate.  This  neutral 
humus  is  insoluble  in  water  and  organic  solvents,  unchanged 
by  ammonium  hydroxide,  but  partly  decomposed  by  sodium 
and  potassium  hydroxides,  forming  the  humates  of  the 
alkalies,  soluble  in  water.  When  treated  with  a  mineral 
acid  like  hydrochloric,  the  humus  is  decomposed,  forming 
humic  acid  insoluble  in  water,  and  calcium  chloride  soluble 
in  water.  On  further  treatment  of  the  soil  with  ammonium 
hydroxide,  the  humic  acid  forms  ammonium  humate  soluble 
in  water. 

121.  Functions  of  Organic  Matter. — In  considering  the 
functions  of  the  organic  matter  in  the  soil  it  should  be  re- 
membered (Section  113)  that  there  are  really  two  kinds  of 
organic  matter:  First,  the  active  or  decomposing  organic 
matter  which  is  constantly  changing,  with  the  production  of 
organic  acids,  carbon  dioxide,  water,  and  mineral  salts,  and 
the  release  of  nitrogen  locked  up  in  insoluble  form ;  second, 
the  inactive  organic  matter  or  humus,  which  is  a  more  or 
less  stable  "compound"  comparatively  resistant  to  further 
rapid  decay. 

(a)  The  Active  Organic  Matter  serves  important  pur- 
poses in  the  production  of  chemical  compounds  active  in  the 
decomposition  of  mineral  particles;  in  the  formation  of 
nitrates  and  soluble  inorganic  salts  which  serve  as  plant 
foods;  in  increasing  the  moisture-holding  capacity  of  the 
soil;  and  in  improving  the  structure  of  the  soil. 


LOSS  OF  ORGANIC  MATTER  143 

(b)  Inactive  Organic  Matter,  or  Humus,  serves  as  the 
reserve  nitrogen  supply,  decomposing  but  slowly,  and  thus 
decreasing  the  loss  of  nitrogen  as  nitrates  by  leaching.  Its 
decomposition  is  ordinarily  so  slow  that  it  does  not  serve  to 
any  great  extent  as  a  source  of  organic  acids,  carbon  dioxide, 
and  inorganic  salts.  Its  principal  function  is  physical,  in 
that  it  improves  the  water  holding  capacity  very  materially ; 
increases  the  heat  absorption  and  thus  warms  up  the  soil 
earlier  in  the  spring;  improves  the  structure  of  the  soil  by 
loosening  heavy  clays,  and  making  sandy  soils  more  compact. 

In  other  words,  active  organic  matter  has  a  decided 
chemical  effect  in  the  soil,  while  humus  has  an  important 
physical  effect.  This  distinction  is  not  absolutely  definite, 
but  is  generally  true. 

122.  Loss  of  Organic  Matter. — ^The  active  decomposition 
of  organic  matter  in  the  soil  is  of  vast  importance  to  the 
farmer.  It  is  not  wholly  a  question  of  piling  up  reserves  of 
organic  matter,  but  rather  of  continually  renewing  the  supply 
which  is  undergoing  constant  decomposition,  thus  rendering 
mineral  particles  soluble,  freeing  plant  food  from  the  organic 
matter,  and  making  nitrogen  available.  In  addition,  of 
course,  there  must  be  a  fair  amount  of  humus,  particularly 
on  sandy  soils,  for  physical  reasons. 

Active  decomposition  and  loss  of  organic  matter — and 
this  includes  humus — takes  place  most  rapidly  under  in- 
tensive cultivation,  proper  drainage,  and  application  of 
lime  and  commercial  fertilizers.  This  is  just  what  should 
take  place,  but  the  supply  must  just  as  surely  be  renewed 
by  good  applications  of  manure,  and  by  plowing  under  grass, 
clover  stubble,  and  green  manure  crops.  Manure  by  its 
rapid  decomposition  does  not  ordinarily  form  humus  to  such 
an  extent  as  do  the  fine,  numerous  roots  of  grass.  Humus 
accumulates  in  pastures  not  only  because  of  the  fine  roots 
thoroughly  spread  throughout  the  soil,  but  also  because  the 
soil  is  not  cultivated  and  the  organic  matter  is  hence  not  so 
completely  oxidized.  Even  very  heavy  applications  of 
manure  do  not  result  in  increased  content  of  organic  matter 
and  humus,  and  consequently  are  not  economical.  It  is 
better  to  put  on  reasonable  applications  (say  6  to  10  tons 


144  THE  SOIL:  ORGANIC  MATTER 

every  two  or  three  years)  and  supplement  with  hay  stubble 
or  green  manure. 

123.  Nitrification. — As  has  been  noted  several  times, 
organic  matter  serves  as  the  source  of  nitrogen  for  crop 
plants.  But  before  this  organic  nitrogen  can  be  used  by 
plants  it  must  undergo  a  change  to  nitrates  (Section  54), 
for  most  of  the  organic  nitrogen  is  protein  in  character,  and 
hence  insoluble  and  unavailable  to  crop  plants. 

The  process  by  which  organic  nitrogen  is  changed  to 
nitrates,  and  thereby  made  available  to  crops,  is  bacterial 
in  character,  and  is  generally  called  nitrification,  although 
it  really  takes  place  in  three  steps,  the  first  called  ammoni- 
fix;ation  and  the  last  two  nitrification  proper.  Oxygen  is 
necessary  for  these  changes  to  take  place,  hence  the  impor- 
tance of  thorough  aeration  to  produce  nitrates  from  the 
nitrogen  reserves  in  the  soil. 

(a)  Ammonification  is  brought  about  by  many  of  the 
bacteria  in  the  soil  and  is  caused  by  the  proteolytic  enz;yTnes 
of  the  bacteria  first  breaking  down  the  proteins  into  simpler 
compounds,  and  further  decomposing  or  hydrolyzing  them 
into  ammonia  among  other  products.  Some  of  the  bacteria 
producing  ammonia  use  it  as  a  source  of  nitrogenous  food, 
others  leave  it  merely  as  a  by-product. 

(6)  Nitrification  Proper  is  a  distinct  bacterial  oxidation 
of  ammonia  to  nitrous  acid,  and  of  nitrous  to  nitric  acid. 
There  are  definitely  known  two  kinds  of  organisms  which 
oxidize  ammonia  to  nitrous  acids,  and  they  are  called  nitrous 
or  nitrite  bacteria.  The  equation  for  this  reaction  may  be 
expressed  as  follows: 

2NH3+  302  =  2HN02+  2H2O. 

There  is  only  one  kind  of  organism  oxidizing  nitrous  acid 
to  nitric  acid,  called  the  nitric  or  nitrate  bacteria.  The 
following  equation  represents  the  reaction: 

2HN02+02=2HN03. 

The  amount  of  ammonia  or  nitrous  acid  in  the  soil  at  any 
one  time  is  very  small  because  the  ammonia  is  changed  very 
rapidly  to  nitrous  acid  and  the  nitrous  acid  to  nitric  acid, 


DENITRIFICATION  145 

Particularly  is  it  difficult  to  detect  traces  of  nitrous  acid 
because  the  nitrous  and  nitric  organisms  work  together,  the 
latter  using  up  nitrous  acid  as  soon  as  it  is  formed. 

It  is  claimed  that  there  is  one  kind  of  bacteria  which 
oxidizes  ammonia  directly  to  nitric  acid,  but  its  identity  is 
not  completely  established. 

These  nitrifying  organisms,  the  nitrous  and  the  nitric, 
obtain  their  energy  by  this  oxidation  process,  and  also  utilize 
the  ammonia  and  nitrous  acid  respectively  as  food  for 
growth.  When  this  happens,  as  whenever  bacteria  use  soluble 
nitrogenous  compounds  as  food,  some  nitrogen  is  converted 
into  protein  and  rendered  insoluble  and  unavailable  to  plants 
until  acted  upon  by  bacteria,  as  in  the  first  instance.  More- 
over, these  bacteria  utilize  only  inorganic  food.  From 
carbon  dioxide  they  manufacture  their  cellular  substances  of 
an  organic  nature.  The  synthesis  is  brought  about  not  by 
chlorophyl  but  by  the  oxidation  of  ammonia  and  nitrous 
acid.  Hence  organic  matter  is  not  essential  for  these  bacteria, 
and  in  fact  too  much  soluble  organic  matter  interferes  with 
their  growth.  This  does  not  happen  in  ordinary  farm  soil, 
but  is  a  serious  matter  at  times  in  soils  very  intensively 
fertilized  with  manure  and  sewage,  like  greenhouse  and 
truck  soils. 

It  is  to  be  noted  that  the  free  acids  themselves  are  the 
products  of  these  bacteria.  In  the  presence  of  bases  or  basic 
carbonates  the  acids  are  neutralized.  Since  calcium  car- 
bonate is  the  principal  acid  neutralizing  substance  in  the 
soil,  nitric  nitrogen  occurs  in  most  soils  as  calcium  nitrate, 
although  some  of  the  acid  is  neutralized  by  magnesium  car- 
bonate and  potassium  carbonate.  If  there  is  not  sufficient 
basic  material  to  neutralize  the  acids  as  they  are  formed,  the 
bacteria  are  rendered  inactive  or  are  killed  by  the  excess  of 
acid.  Other  conditions  for  their  growth  are  much  the  same 
as  mentioned  for  bacteria  in  general  (Section  116,  a). 

124.  Denitrification. — A  process  just  the  opposite  of  nitri- 
fication is  denitrification,  which  results  in  a  loss  of  nitrogen. 
Under  anaerobic  conditions  and  in  the  presence  of  large 
quantities  of  easily  decomposed  organic  matter,  there  are 

several  species  of  bacteria  which   can   reduce  nitrates  to 
10 


146  THE  SOIL:  ORGANIC  MATTER 

nitrites,  to  ammonia,  and  to  free  nitrogen.    The  following 
equations  illustrate  the  reactions: 

2HN03=2HN02+02 
4HN02  =  2H2O  +  2N2  +3O2 
HNO3+  H2O  =  NH3+  2O2. 

These  bacteria  can  live  under  aerobic  conditions,  in  which 
case  they  use  free  oxygen  for  their  respiration,  but  under 
anaerobic  conditions  they  use  the  oxygen  removed  from 
nitrates.  The  oxygen,  whether  from  the  air  or  from  nitrates, 
they  use  in  oxidizing  organic  matter  which  is  necessary  for 
their  growth.  The  denitrifiers  occur  in  manure  and  on  straw 
to  a  considerable  extent,  but  are  not  responsible  for  loss  of 
nitrogen  under  ordinary  farming  conditions.  In  cases  of 
excessive  applications  of  manure  in  addition  to  nitrates, 
or  in  greenhouses  where  soils  are  very  moist  and  large 
quantities  of  organic  matter  are  present,  nitrates  may  be 
reduced.  In  any  conditions  where  soils  are  compact  or  very 
wet  so  there  is  no  aeration,  and  where  excessive  quantities 
of  decomposing  organic  matter  are  present  in  addition  to 
nitrates,  there  denitrification  may  occur.  It  is,  however,  not 
a  condition  that  occurs  frequently  enough  to  cause  anxiety 
over  loss  of  nitrogen.  In  any  event,  where  only  nitrites  and 
ammonia  are  the  products,  loss  does  not  occur,  for  these 
compounds  may  be  later  oxidized  back  to  nitrates.  Only 
free  nitrogen  is  a  total  loss. 

125.  Nitrogen  Fixation. — In  the  discussion  of  nitrogen 
for  the  use  of  plants,  it  has  been  noted  that  the  source  of 
nitrogen  is  the  organic  matter  of  the  soil ;  that  in  the  decom- 
position processes  most  of  it  is  made  available  but  some  may 
be  lost  to  the  air;  that  after  entering  the  plant  it  is  used 
in  tissue  building  and  goes  largely  to  the  seed.  After  the 
plant  dies  that  part  which  is  left  on  the  field  serves  as  organic 
nitrogen  for  bacterial  decomposition  again.  That  part  of 
the  plant  which  goes  to  feed  animals  returns  to  the  soil 
sooner  or  later  in  the  form  of  manure,  or  dead  animals,  or 
parts  of  animals.  The  nitrogen  is  continually  travelling  in 
a  circle  with  some  loss.  So  far  no  mention  has  been  made 
of  any  gain. 


NITROGEN  FIXATION  147 

All  nitrogen  in  combination  on  the  earth  came  at  one  time 
or  another  from  the  atmosphere.  The  nitrate  of  soda  beds, 
coal,  and  many  other  forms,  all  owe  their  nitrogen  to  the 
air.  In  other  words,  there  is  and  has  been  some  natural 
agency  for  combining  atmospheric  nitrogen.  Nitrogen  gas 
is  very  inert  and  does  not  combine  easily  with  other  elements. 
A  small  portion  unites  with  oxygen  under  the  influence  of 
lightning.  But  aside  from  this  there  exist  in  the  soil 
certain  bacteria  which  can  combine  nitrogen  from  the  air 
with  carbon,  hydrogen,  and  oxygen,  and  so  put  it  in  a  form 
that  can  be  used.  This  process  by  which  atmospheric 
nitrogen  is  fixed,  or  made  into  stable  compounds,  is  called 
nitrogen  fixation,  and  is  probably  the  most  important  single 
process  taking  place  in  the  soil,  all  things  considered. 

There  are  two  kinds  of  bacteria  which  can  fix  nitrogen: 
First,  those  which  act  independently  of  other  living  things, 
like  most  of  the  soil  bacteria;  and  second,  those  which  act 
most  energetically  when  living  with  some  other  plant.  In 
both  cases  the  bacteria  derive  energy  for  combining  nitro- 
gen from  the  oxidation  of  carbohydrates,  and  for  their  most 
eflficient  work  large  quantities  of  soluble  carbohydrates, 
sugars  probably,  are  necessary.  The  nitrogen  so  fixed  is 
then  used  by  the  bacteria  in  part,  although  more  is  fixed 
than  the  bacteria  need  for  their  own  growth. 

(a)  Non-Symbiotic. — Those  bacteria  which  act  indepen- 
dently are  non-symbiotic  in  character,  that  is,  they  do  not 
live  with  any  other  plant  to  the  mutual  advantage  of  both. 
They  occur  in  most  soils  apparently  and  are  able  to  fix  some 
nitrogen  which  is  left  in  the  soil  after  their  death.  Not 
very  much  is  known  about  these  bacteria,  but  it  is  not  prob- 
able that  in  ordinary  farming  they  play  much  part  in  adding 
nitrogen  to  the  soil. 

(6)  Symbiotic. — ^This  class  is  by  far  the  more  important 
and  is  familiar  to  all  farmers.  The  nodules  on  the  roots  of 
leguminous  plants  like  clover,  alfalfa,  peas,  beans,  and 
vetch,  are  abnormal  root  growths  formed  to  accommodate 
the  colonies  of  these  nitrogen-fixing  bacteria  which  are  living 
with  the  legumes  to  the  mutual  benefit  of  both  (Figs.  33,  34, 
35).    The  legumes  supply  the  bacteria  with  soluble  carbo- 


148 


THE  SOIL:  ORGANIC  MATTER 


Fig.  33.— Red  Clover. 


Fig.  34.— Alfalfa.  - 


Fig.  35. — Cowpea. 

Figs.  33  to  35. — Nodules  on  legumes.     Bureau  of  Plant  Industry,  United 

States  Department  of  Agriculture. 


NITROGEN  FIXATION 


149 


hydrates,  probably  dextrose  or  maltose,  and  by  the  oxidation 
of  this  material  the  bacteria  fix  nitrogen  obtained  from  the 
soil  air  through  the  nodules.  They  not  only  use  some  of  the 
resulting  compounds  for  their  own  growth  but  apparently 
pass  on  a  large  part  of  it  for  the  use  of  the  legumes.  Fig.  36 
shows  the  effect  of  these  bacteria  on  clover  growing  in  soil 
containing  no  nitrates. 


Fig.  36. — Clover  growing  on  soil  containing  no  nitrates.  /.  No  nitrogen 
fixing  bacteria.  //.  Supplied  with  bacteria.  Soils  Department,  Wisconsin 
Station. 

Both  the  bacteria  and  the  legumes  can  utilize  nitrates  in 
the  soil,  but  apparently  the  symbiotic  relationship  is  better 
for  both.  The  bacteria  do  not  fix  nitrogen  when  supplied 
with  nitrate  nitrogen,  nor  do  the  legumes  accumulate  the 
nodules  to  any  extent  when  there  are  sufficient  nitrates 
in  the  soil. 

The  bacteria  are  present  in  the  soil  to  a  considerable 
extent,  and  although  it  is  claimed  they  can,  under  suitable 
conditions,  fix  nitrogen  independently  of  legumes,  they 
apparently  do  not  do  it  readily.  When  legume  roots  are 
present  in  the  soil  these  bacteria  enter  the  root  hairs,  grow 
into  long  gelatinous  threads  which  penetrate  the  various 
cells  of  the  fine  roots,  and  develop  immense  numbers  of 
bacteria.     Their  multiplication  causes  the  peculiar  nodule 


150  THE  SOIL:  ORGANIC  MATTER 

formation  on  the  young  roots.  On  clover  and  alfalfa  the 
nodules  are  very  small  like  a  pinhead  or  a  small  bean,  but 
on  some  beans  and  cowpeas  they  are  very  large,  even  reaching 
the  size  of  baseballs  on  the  velvet  bean.  When  the  legume  is 
harvested  and  the  roots  die  the  nodules  decompose,  the 
accumulated  fixed  nitrogen  going  back  to  the  soil.  The 
bacteria  remain  for  the  most  part  inactive  until  more  legumes 
are  grown.  The  amount  of  nitrogen  added  to  the  soil  by 
plowing  under  the  legume  crop  varies  considerably  with  the 
crop,  season,  and  condition  of  soil,  but  it  is  safe  to  say  that 
the  ordinary  clover  crop  adds  40  to  50  pounds  per  acre,  and 
alfalfa  75  to  100  pounds  per  acre. 

Although  there  seems  to  be  evidence  that  most  of  these 
symbiotic  bacteria  belong  to  but  one  or  two  species,  as  a 
matter  of  practical  fact  they  are  so  differentiated  by  habit 
of  growth  that  there  are  several  classes.  For  instance,  the 
bacteria  which  live  on  alfalfa  roots  are  not  fitted  to  live  on 
red  clover  roots,  nor  do  the  bacteria  of  beans  live  on  vetch 
roots.  Not  every  legume  has  its  own  special  bacteria,  how- 
ever, for  alfalfa  and  sweet  clover  can  interchange  bacteria; 
white,  alsike,  and  red  clovers  apparently  have  the  same 
bacteria;  the  vetches  all  seem  to  use  the  same  organism. 

As  far  as  crop  plants  are  concerned  only  legumes  have 
nitrogen  fixing  bacteria  on  their  roots,  but  there  are  some 
plants  such  as  the  alder,  New  Jersey  tea,  buffalo  berry, 
sweet  fern,  and  a  few  others  which  also  have  bacterial  nodules 
on  their  roots.  The  importance  of  this  fact  lies  in  the 
ability  of  waste  lands  to  accumulate  nitrogen  through  the 
agency  of  wild  plants. 

1 26 .  Inoculation. — Practically  all  soils  contain  the  nitrogen 
fixing  bacteria  for  the  common  clovers,  peas,  and  beans,  so 
that  a  failure  to  have  nodules  develop  on  these  legumes  is 
due  rather  to  other  causes  than  to  lack  of  the  bacteria  in  the 
soil.  For  example,  lime  may  be  lacking,  the  soil  may  need 
drainage,  too  much  available  nitrogenous  compounds  like 
nitrates  may  be  present,  plant  diseases  may  infect  the 
legumes.  But  where  a  new  legume  is  tried,  such  as  alfalfa 
or  serradella,  and  the  crop  fails  under  ordinarily  beneficial 
conditions,  it  may  be  necessary  to  inoculate  the  soil  with 
the  proper  bacteria. 


INOCULATION 


151 


This  can  be  done  by  applying  200  to  500  pounds  of  surface 
soil  from  some  field  where  the  crop  in  question  has  produced 
nodules,  or  where  a  similar  crop  has  succeeded.  The  soil 
should  be  harrowed  in  at  once  to  prevent  the  sunlight  from 
killing  the  bacteria.  In  the  case  of  alfalfa,  soil  from  a  road- 
side where  sweet  clover  grows  is  satisfactory.  This  practice 
of  course  may  introduce  weed  seeds  or  plant  diseases  into 
the  soil  and  for  that  reason  is  not  always  satisfactory. 

It  is  possible  to  get  pure  cultures  of  the  bacteria  at  some 
of  the  experiment  stations,  and  from  some  commercial 
sources  (Fig.  37).  These  cultures  can  be  mixed  with  water 
and  the  seeds  soaked  in  it  before  planting.    The  bacteria  cling 


4 


n 


m\ 


Fig.  37. — Cultures  for  Legume  Inoculation.     Bacteriological  Department, 
Virginia  Station. 


to  the  seeds  and  infect  the  roots  when  the  seeds  germinate. 
The  trouble  with  this  method  is  to  get  cultures  which  are 
fresh.  Many  preparations  put  out  by  commercial  firms  and 
the  scheme  of  the  United  States  Department  of  Agriculture 
for  sending,  out  the  bacteria  dried  on  cotton  have  failed 
because  the  bacteria  were  dead  when  inoculation  was 
attempted. 

It  must  not  be  thought  that  inoculation  alone  is  the  easy 
way  to  obtain  nitrogen  from  the  air  and  that  it  will  work  on 
any  crop.  There  are  people  who  think  it  is  a  complete 
fertilizer  in  vest  pocket  form;  that  corn  or  oats  can  be 
inoculated  and  will  gather  their  own  nitrogen!  It  is  not  a 
complete  fertilizer  and  will  not  help  any  but  leguminous 


152  THE  SOIL:  ORGANIC  MATTER 

crops,  and  then  only  if  the  inoculating  material  contains 
living  bacteria.  The  average  farmer  will  probably  never 
need  to  inoculate  his  legume  crop.  Failure  to  get  a  crop  is 
usually  due  to  some  other  cause  more  or  less  easily  remedied. 

EXERCISES 

1.  How  could  you  isolate  humus  from  an  acid  soil?  from  an  alkaline  soil? 

2.  In  what  two  ways  might  the  nitrogen  of  the  air  become  a  constituent 
part  of  a  legume  protein? 

3.  Trace  nitrogen  from  an  atmospheric  element  until  it  becomes  part  of 
an  organic  substance  found  in  leguminous  plants;  thence  until  it  becomes 
nitrates  in  the  soil;  thence  through  protein  formation  in  some  plant  other 
than  a  legume;  thence  until  it  is  deposited  in  the  seed  of  some  plant;  thence 
until  it  becomes  atmospheric  nitrogen. 

4.  How  do  carbon  dioxide  and  water  affect  nitrification  and  nitrogen 
fixation? 

5.  Distinguish  among  humus,  organic  matter,  acid  humus  and  neutral 
humus.  To  what  extent  are  these  four  materials  alike  or  unlike  chemically 
and  physically? 

6.  Why  are  nitrification  and  nitrogen  fixation  such  important  phenomena? 

7.  State  five  ways  in  which  respiration  differs  from  photosynthesis,  and 
three  ways  in  which  respiration  differs  from  intermolecular  respiration. 

8.  Show  that  the  nitrogen  applied  as  nitrates  was  once  atmospheric 
nitrogen. 

9.  Explain  in  detail  how  alfalfa  differs  from  potatoes  in  the  way  it  builds 
up  proteins. 

10.  In  detail  state  how,  when  and  where  organic  matter  can  be  changed 
into  humus. 

11.  What  condition  is  best  for  the  soil,  complete  absence  of  oxygen,  an 
excess  of  oxygen,  or  a  happy  medium  in  respect  to  oxygen?  In  detail, 
explain  why. 

12.  To  what  extent  are  acid  and  neutral  humus  alike  chemically  and 
physically? 

13.  What  properties  do  proteins  have  that  make  their  nitrogen  not 
directly  available? 

14.  Define  symbiosis.  Just  what  do  brcteria  give  legumes  and  what  do 
the  legumes  give  in  return?     Why  this  exchange? 

REFERENCES 

Bulletins  of  Bureau  of  Soils,  U.  S.  Dept.  of  Agriculture. 

Cameron.     The  Soil  Solution. 

Hall.     The  SoU. 

Halligan.     Soil  Fertility  and  Fertilizers. 

Hilgard.     Soils. 

Hopkins.     Soil  Fertility  and  Permanent  Agriculture. 

Lyon  and  Fippin.     Soils. 

Russell.     Soil  Conditions  and  Plant  Growth.' 

Van  Slyke.     Fertilizers  and  Crops. 

Whitson  and  Walster.     Soils  and  Soil  Fertility. 


CHAPTER  VII 
THE  SOIL:  INORGANIC  MATTER 

In  the  previous  chapter  the  discussion  of  organic  matter 
in  the  soil  brought  out  the  fact  that  it  was  the  immediate 
source  of  nitrogen  for  plants.  The  other  necessary  elements 
which  are  derived  from  the  soil  come,  originally  at  least, 
from  the  mineral  particles  or  inorganic  portion  of  the  soil. 
The  organic  matter  in  its  decomposition  furnishes  acids  which 
are  important  agents  in  the  solution  of  mineral  particles. 
Other  factors  in  the  changes  of  mineral  particles  are  the 
gases  present  in  the  soil. 

127.  Soil  Gases. — ^The  pore  spaces  of  a  soil  are  filled, 
part  of  the  time  with  gases,  and  part  of  the  time  with  water. 
The  latter  condition  happens  only  after  a  rain,  and  in  a  soil 
of  good  structure  does  not  last  very  long.  The  water  running 
down  into  the  country  drainage  is  followed  by  atmospheric 
gases.  From  the  decomposing  organic  matter  gases  are 
added  to  those  already  present,  and  at  the  same  time  some 
gases  are  withdrawn  by  absorption  from  the  soil  atmosphere. 
Certain  chemical  reactions  also  involve  changes  in  the 
composition  of  soil  atmosphere.  It  has  been  found  that 
nitrogen  varies  but  little,  existing  in  the  soil  in  about  the 
same  proportion  that  it  does  in  the  air,  namely  78  per  cent. 
(Section  109). 

Oxygen  varies  from  10  to  20  per  cent.,  whereas  in  the 
air  it  runs  rather  constantly  at  21  per  cent.  This  difference 
is  due  to  changing  rates  of  oxidation  resulting  from  bacterial 
action  on  the  organic  matter,  as  well  as  to  ordinary  chemical 
oxidation  of  minerals  in  the  soil.  The  amount  of  carbon 
dioxide  varies  inversely  with  the  oxygen  content,  running 
from  about  11  to  1  per  cent.  As  oxygen  is  used  up  in  oxidiz- 
ing organic  matter,  carbon  dioxide  is  evolved.  Ordinarily  the 
disappearance  of  oxygen  causes  the  appearance  of  an  equal 
volume  of  carbon  dioxide.  Intermolecular  or  anaerobic 
oxidation  is  not  sufficient  in  ordinary  soils  to  cause  much 

(153) 


154  THE  SOIL:  INORGANIC  MATTER 

change  in  the  composition  of  the  soil  gases.  In  other  words 
the  amount  of  oxygen  and  carbon  dioxide  together  equal 
21  per  cent,  rather  constantly.  In  the  air  they  amount 
to  21.02  per  cent. 

Decomposing  organic  matter  is  the  principal  factor  in  the 
variation  in  composition  of  soil  gases,  and  to  this  cause  also 
is  due,  especially  in  soils  more  or  less  water-logged,  the 
presence  of  methane  and  hydrogen  sulphide;  but  these  gases 
are  rare  constituents  in  any  ordinary  soil  in  good  condition. 
Other  constituents  are  not  worth  considering. 

As  to  the  value  of  soil  gases  in  decomposing  mineral 
particles,  it  will  be  found  later  that  carbon  dioxide  and 
oxygen  are  the  most  active  agents.  A  solution  of  carbon 
dioxide  in  water  is  by  far  the  most  active  solvent  for  minerals 
which  the  soil  produces.  Of  course  sulphuric  and  nitric 
acids  which  result  from  decomposing  organic  matter  are 
more  powerful  reagents  ordinarily,  but  their  occurrence  is 
very  slight  compared  to  that  of  carbonic  acid,  which  though 
rated  a  weak  acid  is  always  present  in  large  quantities  in 
practically  all  soils.  Decaying  organic  matter  has  been  esti- 
mated to  supply  through  bacterial  action  to  a  depth  of  eight 
inches,  about  1  ton  of  carbon  dioxide  per  acre  per  year.  When 
dissolved  in  water  this  makes  a  very  respectable  amount  of 
solvent.  Organic  acids,  together  with  sulphuric  and  nitric 
acids,  are  produced  in  very  much  smaller  amounts,  and 
being  very  dilute  have  not  the  effect  that  carbon  dioxide 
has,  although  these  reagents  are  to  be  reckoned  with  in 
considering  mineral  decomposition  and  solubility. 

128.  Soil  Solvents. — ^The  soil  moisture  which  acts  on  the 
mineral  particles  in  the  soil  consists  primarily,  of  course,  of 
water.  Pure  water  dissolves  ordinary  minerals  but  slightly, 
except  gypsum  and  sodium  chloride,  of  which  the  latter 
occurs  in  normal  soils  more  as  a  decomposition  product 
than  as  an  original  mineral.  In  the  soil,  however,  water  is 
never  pure.  Carbon  dioxide  is  always  present  from  the  decay 
of  organic  matter.  Living  plant  roots  excrete  carbon  dioxide 
because  of  respiration,  and  the  soil  moisture  immediately 
around  such  roots  is  fairly  well  concentrated  in  this  con- 
stituent. The  growing  of  plants  on  a  polished  slab  of 
marble — calcium  carbonate — or  on  one  of  feldspar  leaves  a 


SOIL  MINERALS  165 

fine  tracery  of  the  roots  caused  by  the  solvent  action  of  the 
carbon  dioxide  excreted.  Carbon  dioxide  is  soluble  in  pure 
water  to  the  extent  of  about  1  part  in  GOO  parts  of  water. 
The  presence  of  soluble  salts  reduces  its  solubility. 

Oxygen  is  very  generally  present  in  the  moisture  of  well 
aerated  soils,  attacking  minerals  containing  ferrous  iron, 
like  hornblende,  and  breaking  them  down  with  water  and 
carbon  dioxide.  It  is  soluble  to  the  extent  of  about  1  part 
in  20,000  parts  of  water. 

Organic  Acids  like  acetic,  butyric,  and  others  of  a  more 
complex  nature,  all  formed  by  the  bacterial  decay  of  organic 
matter,  particularly  carbohydrates,  dissolve  in  soil  water 
to  a  greater  or  less  extent  and  act  on  many  minerals. 

Inorganic  Acids  like  sulphuric  and  nitric,  formed  from 
sulphur  and  nitrogen  in  organic  matter,  serve  as  very  active 
reagents.  They  are  present,  however,  to  a  very  small 
extent  at  any  one  time. 

Soluble  Salts,  derived  from  various  minerals  such  as 
chlorides,  nitrates,  and  sulphates,  all  have  a  greater  or  less 
effect  on  minerals. 

129.  Soil  Minerals. — In  considering  the  chemical  changes 
by  which  inorganic  plant  food  becomes  available,  it  is 
necessary  to  know  some  of  the  principal  soil  minerals  which 
are  the  source  of  these  elements.  They  will  be  taken  up  and 
discussed  in  groups  according  to  the  element  or  elements 
which  they  supply.  In  addition  there  will  be  discussed 
the  minerals  of  a  few  elements  which  are  thought  not  to  be 
essential  and  yet  which  occur  very  commonly  in  plants, 
or  which  have  some  effect  in  the  soil. 

(a)  Phosphorus  Minerals. — ^The  principal  mineral  con- 
taining phosphorus  is  apatite,  CasCPOjsCl  or  F.  To  show  its 
chemical  structure  better  it  may  be  written  graphically: 

o=p^o/ 

>Ca 
0=P^O— Ca— C1(F> 

0=P^0\ 


156  THE  SOIL:  INORGANIC  MATTER 

It  occurs  in  hexagonal  prisms  frequently  of  very  small 
size,  almost  like  needles,  and  green  or  red  in  color. 

This  compound  is  practically  insoluble  in  water  but  under 
the  action  of  water  and  carbon  dioxide  it  slowly  dissolves, 
possibly  according  to  the  following  equation: 

2Cat(PO0»Cl  +  I2CO2+  I2H2O  =  3CaH4(P04)2+  6CaH2(COs)2+  CaCh. 

Most  of  the  phosphorus  in  soils,  however,  occurs  in  an 
amorphous,  secondary  form  possibly  derived  from  apatite, 
expressed  by  the  formula  Ca3(P04)2  and  called  tricalcium 
phosphate.  This  compound  in  the  presence  of  small  amounts 
of  carbon  dioxide  in  water  changes  to  the  dicalcium  phos- 
phate, thus: 

Ca»(P04)2+  2CO2+  2H2O  =  Ca2H2(P04)2+  CaH2(C03)2. 

In  the  presence  of  more  carbon  dioxide  and  water  it  decom- 
poses to  the  monocalcium  phosphate,  thus: 

Ca3(P04)2+4C02  +  4H2O  =  CaH4(P04)2+  2CaH2(COj.)2. 

Tricalcium  phosphate  is  practically  insoluble  in  pure  water, 
1  part  requiring  50,000  parts  of  water,  whereas  dicalcium 
phosphate  is  soluble  to  the  extent  of  1  part  in  7500  parts  of 
water,  and  monocalcium  phosphate,  1  part  in  100  of  water. 

Soil  water,  of  course,  is  never  pure  water,  having  always 
some  substances  dissolved  in  it,  and  these  substances  in 
solution  tend  to  modify  the  above  solubilities  to  a  slight 
extent;  but  the  figures  serve  to  show  the  relative  solubilities 
of  the  three  forms  of  phosphate.  Dicalcium  phosphate  and 
monocalcium  phosphate,  both  of  them,  can  be  used  by  plants. 
Since  carbon  dioxide  is  so  generally  prevalent  in  soil  water 
and  can  dissolve  tricalcium  phosphate,  it  is  safe  to  say 
that  all  compounds  of  phosphorus  with  calcium  are  available 
forms  of  phosphorus  for  plant  use. 

Phosphorus  also  occurs  as  more  or  less  indefinite  com- 
pounds of  iron  phosphate,  FeP04,  and  aluminium  phosphate, 
AIPO4,  both  very  insoluble  in  water,  or  in  water  and  carbon 
dioxide,  or  in  any  other  ordinary  soil  solution,  unless  calcium 


SOIL  MINERALS  157 

is  present.  Where  calcium  bicarbonate  is  in  solution  in  the 
soil  water  these  phosphates  are  slowly  changed  as  follows: 

2FeP0i+  CaHj(COi)i  +  4HsO  =  2Fe(0H).+  CaH4(P04)i+  2C0j. 

This  emphasizes  the  importance  of  having  calcium  carbonate 
or  lime  in  the  soil.    Aluminium  phosphate  acts  similarly. 

(6)  Potassium  Minerals. — Since  these  minerals,  and  in 
addition  most  of  those  of  calcium,  magnesium,  and  iron, 
belong  to  that  principal  group  of  minerals  called  silicates, 
it  will  help  to  understand  their  structure  if  a  brief  survey 
is  made  of  the  silicic  acids  from  which  they  are  derived. 

Silicic  Acids. — Normal  or  orthosilicic  acid  is  H4Si04, 
written  graphically: 

H— O  O— H 

\   / 
Si 

/  \ 

H— O  O— H 

By  the  elimination  of  one  molecule  of  water  there  is  formed 
metasilicic  acid,  thus: 

H4Si04— H2O  =H2Si03  or: 
O— H 

/ 
0  =  Si 

\ 

O— H 

metasilicic  acid. 

By  the  elimination  of  three  or  more  molecules  of  water  from 
two  or  more  molecules  of  orthosilicic  acid  there  are  formed 
polysilicic  acids,  of  which  the  disilicic  and  trisilicic  acids  are 
the  commonest.    They  are  formed  thus: 

1.  2H4SiO«  —  3H2O  =  HsSijOs  or: 
O— H 

/ 
0=Si 

\ 
O 

/ 
0=Si 

\ 
O— H 
disilicic  acid. 


158  THE  SOIL:  INORGANIC  MATTER 


'..  3HSiO 

4  — 4H20=H4Si.08,  or: 

H- 

-0            O— H 

\    /      " 

Si 

/    \ 

0         o 

\  / 

Si 

/  \ 

0            0 

\  / 

Si 

/  \ 

H- 

-0            0— H 

trisiiicic  acid. 

These  silicic  acids  are  either  unknown  or  but  little  known 
in  the  free  condition  but  their  salts  are  very  common  among 
the  silicates  which  constitute  most  of  the  soil  minerals. 

The  most  important  potassium  silicate  is  a  double  tri- 
silicate  of  potassium  and  aluminium  called  orthoclase  or  the 
potash  feldspar.  Its  formula  is  K2Al2(Si308)2.  It  is  frequently 
written  K20.Al203.6Si02  which  shows  its  composition  but 
not  its  chemical  structure.    Written  graphically  it  is: 


It  occurs  in  monoclinic  crystals  of  flesh-red,  yellow,  or  white 
color.    In  pure  water  orthoclase  is  but  very  slighly  soluble, 


SOIL  MINERALS  159 

but  in  water  containing  carbon  dioxide  it  decomposes  as 
follows : 

K»A1j(SuO.)2+  COi+2HtO  =  Al2(OH)*Si20»+  4SiO»+  KiCOi. 

Its  solubility  in  pure  water  is  1  part  in  37,000;  in  water 
saturated  with  carbon  dioxide,  1  part  in  4000. 

From  the  above  equation  it  is  to  be  noted  that  the  potas- 
sium goes  into  solution  as  potassium  carbonate  and  it  is 
this  form  which  supplies  the  plant  with  most  of  its  potassium. 
It  is  also  to  be  observed  that  a  new  silicate  is  formed.  This 
is  a  hydrated  disilicate  of  aluminium  and  is  called  kaolinite, 
the  graphic  formula  of  which  is: 

o— H 
/ 

O— Al 

/  \ 

0=Si  O— H 

\ 
O 

/ 
0=Si  O— H 

\  / 

O— Al 

\ 
O— H 

It  is  a  compact  or  mealy  mass  with  greasy  feel  when  wet, 
very  plastic,  and  white,  yellow,  brown,  red,  or  blue  in  color. 
This  particular  process  of  decomposition  by  which  kaolinite 
is  formed  is  called  kaolinization  and  is  common  to  very  many 
silicates.  It  is  one  of  the  most  important  soil  reactions,  for 
not  only  is  plant  food  made  available  by  it,  but  in  addition 
the  soil  structure  is  modified  by  kaolinite,  the  basis  of  clay. 
The  mechanical  mixture  of  kaolinite  and  silica  formed  in 
the  above  reaction  is  called  kaolin  or  potter's  clay.  Varying 
amounts  of  silica  are  present,  some  being  dissolved  and 
washed  away  in  the  soil. 

The  potassium  in  orthoclase  is  also  said  to  be  made  avail- 
able by  another  reaction  caused  by  calcium  bicarbonate,  thus: 

KjAl2(Si,0.)j+  CaHi(COi)s  =  CaAl2(Si,08)2+  2KHC0». 

This  shows  the  importance  of  having  calcium  carbonate  in 
the  soil.  (Compare  the  effect  of  calcium  bicarbonate  on 
iron  phosphate.  Section  129,  a). 


160  THE  SOIL:  INORGANIC  MATTER 

Leucite  is  another  potassium  mineral  which  has  the 
formula  KAl (8103)2 — a  metasilicate.  It  occurs  in  trans- 
lucent to  opaque  grains  of  gray  to  white  color.  The  potas- 
sium becomes  slowly  available  under  the  action  of  water 
and  carbon  dioxide. 

Another,  potassium  mineral  that  is  very  common  and  very 
familiar  to  nearly  everybody  is  potash  mica  or  muscovite. 
The  thin,  transparent  leaves  that  very  easily  cleave  are  too 
common  to  need  description.  This  is  the  white  mica.  It  is  an 
orthosilicate  the  formula  for  which  is  H2(K  or  Na)Al3(Si04)3. 
It  might  be  called  an  acid  salt  since  the  hydrogen  atoms 
replace  bases — that  is,  they  are  true  acid  hydrogen  atoms. 
It  is  very  resistant  to  the  action  of  soil  reagents  but  does 
change  very  slowly  under  the  action  of  water  and  carbon 
dioxide,  allowing  potassium  to  go  into  solution. 

(c)  Sulphur  Minerals. — The  principal  sulphur  mineral  is 
gypsum  or  land  plaster,  CaS04.2H20.  It  is  soft,  white, 
granular,  or  compact,  sometimes  silky  and  fibrous.  Occasion- 
ally it  is  crystalline.  It  is  soluble  in  water  to  the  extent  of 
1  part  in  400.  On  being  heated  to  130°  C.  it  loses  one  mole- 
cule of  water  and  becomes  "plaster  of  Paris,"  which  has  the 
power  of  reabsorbing  the  lost  molecule  of  water  and  "setting" 
to  gypsum  again.  This  property  is  made  use  of  in  making 
casts,  etc.  There  is  another  sulphur  mineral  called  anhy- 
drite which  is  CaS04.    This  is  more  or  less  common. 

(d)  Calcium  Minerals. — Aside  from  apatite  and  gypsum 
which  contain  calcium  there  are  a  number  of  important 
calcium  minerals.  By  far  the  most  common  is  calcite, 
CaCOs.  This  occurs  as  white  or  yellowish,  transparent 
crystals  of  many  shapes,  but  the  amorphous  variety  known 
as  limestone  is  the  commonest,  and  is  too  well  known  to  need 
description.  It  occurs  pure,  and  with  magnesium,  when  it 
is  called  dolomite,  Ca.Mg(C03)z: 

O — Ca — o 

/  \ 

o=c  c=o 

\  / 

O — Mg — O 

Calcium  carbonate  is  soluble  in  pure  water  only  to  the  extent 
of  1  part  in  20,000,  but  when  the  water  contains  carbon 


SOIL  MINERALS  161 

dioxide  to  saturation  the  calcium  carbonate  is  soluble  to  the 
extent  of  1  part  in  1000  of  water,  being  changed  to  the  acid 
carbonate,  thus: 

CaCOj+  HiO+  CO2  =  CaHj(CO»)j. 

This  form  of  calcium  is  the  most  important  in  the  soil, 
although  some  of  the  more  soluble  silicates  supply  small 
amounts  of  this  element. 

Anorthite  or  the  lime-feldspar  is  an  orthosilicate  of  calcium 
and  aluminium,  CaAl2(Si04)2,  which  slowly  decomposes 
under  the  action  of  water  and  carbon  dioxide  to  kaolinite 
and  calcium  bicarbonate. 

(e)  Iron  Minerals. — Iron  occurs  largely  as  the  hydrated 
ferric  oxide,  Fe203.xH20,  in  surface  soils.  There  are  a  number 
of  minerals  of  this  kind,  of  which  limonite  is  the  most  common. 
It  is  an  amorphous,  loose  to  compact,  yellow  or  brown  mineral, 
occurring  fairly  well  disseminated  in  soils.  Its  formula  is 
Fe403(OH)6,  graphically: 

/OH 


HO— Fe 

o 

y 

o 

HO— Fe^ ' 


HO— Fe<: 


\ 

o 

HO— Fe/ 

^OH 

Limonite  is  derived  from  silicate  minerals  containing  iron, 
hornblende  for  example.  This  occurs  in  columnar  and  gran- 
ular crystals  of  green,  brown,  or  black  color.  It  is  a  meta- 
silicate  of  any  two  or  sometimes  more  of  the  following  bases : 
Calcium,  magnesium,  iron,  and  aluminium.  The  iron  may 
be  ferrous  or  ferric.  Under  the  action  of  water  and  carbon 
dioxide,  carbonates  or  bicarbonates  of  the  bases  are  formed, 
except  ferric  iron  which  is  set  free  as  such,  usually  in  the 
hydrated  form  and  becomes  limonite  or  similar  minerals. 
If  the  iron  is  ferrous  it  is  changed  to  carbonate  first  but 
11 


162  THE  SOIL:  INORGANIC  MATTER 

oxidizes  almost  instantly,  if  in  aerated  soils,  to  the  hydrated 
oxide.  If,  however,  the  decomposition  takes  place  in  sub- 
soils and  in  water-logged  soils,  ferrous  carbonate  may  remain 
as  siderite,  FeCOa.  Iron  compounds  give  the  yellow,  red, 
and  brown  color  to  soils  when  it  is  not  masked  by  humus. 
A  phosphate  mineral  is  vivianite,  Fe3(P04)2,  a  bluish-green, 
earthy  mass. 

(/)  Magnesium  Minerals. — Some  of  the  magnesium  in 
soils  is  derived  from  dolomite,  already  mentioned  under  the 
calcium  minerals.  There  are  also  many  silicates  containing 
magnesium,  hornblende,  already  mentioned,  and  biotite  or 
black  mica,  an  orthosilicate  of  aluminium,  magnesium,  hydro- 
gen, and  potassium,  thus:  (H  or  K)2(Mg  or  Fe)2Al2(Si04)3- 
This  mineral  is  similar  to  muscovite  or  white  mica,  except 
as  to  color,  which  is  dark  green  or  black. 

(g)  Silicon  Minerals. — All  of  the  silicate  minerals  con- 
tain silicon,  of  course,  but  quartz,  or  Si02,  is  the  only  one  to 
be  considered  here.  It  is,  next  to  feldspar,  the  most  common 
mineral  in  the  earth's  crust  and  occurs  in  many  varieties 
and  all  colors  from  transparent  and  white  to  red,  blue, 
green,  and  brown.  Small  quantities  of  impurities  give  the 
color  to  it.  Ordinarily,  however,  it  is  a  hard,  brittle  mineral, 
clear  to  white,  and  in  hexagonal  crystals  of  all  sizes,  although 
frequently  amorphous.  Sandstone  and  quartzite  are  massive 
varieties  of  quartz.  It  is  ordinarily  very  insoluble,  but  some 
varieties  dissolve  appreciably  to  the  silicic  acids. 

(h)  Sodium  Minerals. — Common  salt,  or  halite,  NaCl,  is 
the  most  familiar  mineral  of  both  sodium  and  chlorine,  but 
it  does  not  occur  to  any  extent  in  agricultural  soil,  being 
confined  to  beds  located  in  many  parts  of  the  world.  Albite, 
or  the  soda  feldspar,  is  a  silicate  mineral  of  soda  and  is  the 
counterpart  of  orthoclase,  being  Na2Al2(Si308)2.  It  occurs 
in  white  granular  masses  or  plates.  Its  solubility  is  similar 
to  that  of  orthoclase. 

(i)  Chlorine  Minerals. — Halite  mentioned  above  is  the 
only  one  of  importance.  There  is  very  little  chlorine  in 
soils  ordinarily. 

(j)  Aluminium  Minerals. — ^The  feldspars  and  many 
other  silicates  contain  aluminium,  and  these  break  down  as 


FACTORS  OF  SOLUBILITY  163 

noted  above  to  kaolinite,  which  is  an  aluminium  mineral. 
In  addition  there  are  bauxite,  Al20(OH)4, 

OH 

/ 

Al— OH 

\ 
O 

'         / 
Al— OH 

\ 
OH 

rounded  grains  or  clay-like  masses,  white  or  yellowish  in 
color;  and  wavellite,  Al3(OH)3(P04)2, 

/    >AI— OH 
0=P— O'^ 
\ 

>A1— OH 
O^ 

/ 
O  =P— 0\ 

\    >A1— OH 

(y 

radiating  crystals  occurring  in  hemispherical  masses. 

130.  Factors  of  Solubility. — From  the  above  discussion  of 
the  solubilities  and  decomposition  products  of  soil  minerals 
it  might  be  thought  that  solution  was  easy  and  the  reactions 
fairly  simple.  But  it  must  be  emphasized  that  under  actual 
conditions  the  reactions  only  approximate  those  indicated. 
That  is,  only  a  part  of  any  mineral  actually  decomposes  as 
far  as  stated.  Reactions  are  not  complete,  and  while  in 
the  case  of  a  feldspar,  for  example,  some  potassium  car- 
bonate and  kaolinite  are  formed,  and  formed  continually 
although  slowly,  much  of  the  mineral  remains  unaltered  and 
some  of  it  decomposes  only  partly.  Intermediate  compounds 
are  formed.  Other  compounds  interfere  and  react  with  the 
original  mineral  or  with  its  decomposition  products.  Much 
more  so  is  this  true  of  more  complex  minerals. 

Temperature  has  a  decided  effect  on  these  reactions  in  the 
soil.     The  higher  the   temperature   the  more   active   the 


164  THE  SOIL:  INORGANIC  MATTER 

decomposition  by  most  solvents  except  carbon  dioxide. 
This  compound  is  less  soluble  in  warm  water  than  in 
cold.  Then,  too,  the  amount  of  water;  the  movement  of 
water,  which  removes  decomposition  products  and  exposes 
fresh  surfaces  to  the  action  of  the  solvents;  the  size  of  soil 
particles;  the  arrangement  of  soil  particles;  the  kind  of  soil 
particles;  all  have  a  decided  effect  on  the  rate  and  amount 
of  decomposition.  Some  minerals  like  feldspar  decompose 
fairly  readily ;  others,  like  mica,  decompose  with  considerable 
difficulty.  And  again,  small  minerals  like  apatite  may  be 
enclosed  within  other  minerals,  like  quartz,  for  example, 
and  soil  solvents  cannot  touch  them.  All  these  factors,  of 
course,  are  in  addition  to  the  amount  of  organic  matter,  the 
rate  of  its  decomposition,  and  the  number  of  bacteria. 

To  sum  up,  then,  the  decomposition  of  mineral  particles 
in  the  soil,  while  it  appears  rather  simple,  is  in  reality  depend- 
ent on  many  factors  which  are  only  more  or  less  controllable 
by  the  farrner.  But  if  he  understands  the  ordinary  progress 
of  favorable  decomposition,  he  can  modify  his  controllable 
factors  accordingly.  He  can  cultivate,  maintain  the  supply 
of  organic  matter,  and  look  after  drainage  or  irrigation  as 
the  case  may  be. 

131.  Absorption. — From  what  has  been  said  it  might  be 
thought  that  when  once  a  plant  food  becomes  soluble  it 
undergoes  no  further  change,  and  if  not  taken  up  at  once  by 
the  plant  is  in  danger  of  being  leached  from  the  soil.  The 
danger  of  leaching  is  by  no  means  as  great  as  might  be 
expected,  and  any  given  plant  food  element  undergoes  a 
great  many  changes  before  it  meets  its  final  fate  in  the 
plant  or  in  the  drainage  water.  Compounds  are  constantly 
going  into  solution  or  being  made  available,  and  going 
out  of  solution  or  being  made  unavailable.  Compounds 
are  also  held  in  the  soil  by  physical  means.  In  other  words 
the  soil  not  only  makes  plant  food  available  from  its  reserve 
stores,  but  it  in  large  measure  prevents  them  from  being 
removed  from  the  soil  by  leaching.  This  process  of  retention 
of  soluble  salts  or  of  elements  in  soluble  compounds  is  called 
absorption,  or  sometimes  fixation.  The  latter  is  not  so  good 
a  name  since  it  may  be  confused  with  nitrogen  fixation  which 


CHEMICAL  ABSORPTION  165 

is  a  very  different  process  (Section  125).  Absorption,  as 
barely  indicated  above,  is  of  two  kinds,  chemical  and  physical. 
132.  Chemical  Absorption. — Some  elements  are  retained 
in  the  soil  by  a  chemical  reaction  which  changes  the  element 
from  a  soluble  compound  into  an  insoluble  compound.  This 
may  take  place  by  double  decomposition  and  subsequent 
precipitation,  or  by  simple  precipitation.  When,  for  example, 
potassium  sulphate  or  potassium  carbonate  in  solution  in  the 
soil  moisture  comes  in  contact  with  an  insoluble  compound 
containing  calcium,  such  as  a  silicate  or  a  humate,  there  is 
an  interchange  of  bases,  the-  potassium  remaining  as  the 
silicate  and  the  calcium  leaching  away  as  the  sulphate 
or  carbonate  (bicarbonate  would  be  the  soluble  form),  thus: 

CaAl2(Si,08)j+  K2COJ+  H2O+CO2  =  K2Al2(Si308)2+  CaH2(C0i)!. 

Or  take  a  compound  like  monocalcium  phosphate.  It  is 
precipitated  by  calcium  bicarbonate  or  iron  hydroxide  as  an 
insoluble  phosphate,  thus: 

CaH4(P04)2  +  2CaH2(C03)2  =  Cas(P04)2  +  4H2O  +  4CO2 

and 

2Fe(0H)i+  CaH4(PO02+  2CO2  =  2FeP04+  CaH2(COs)2+  4H2O. 

In  some  cases  the  reaction  occurs  directly  between  a  solid 
and  a  compound  in  solution.  In  other  cases  two  substances 
in  solution  react  and  an  insoluble  precipitate  results.  In 
one  case  it  is  an  exchange  of  bases,  and  in  this  connection 
it  must  be  noted  that  other  bases  than  potassium  and  calcium 
exchange  places  in  this  way.  Sodium,  magnesium,  and 
ammonium  exchange  with  one  another  and  with  potassium 
and  calcium.  In  the  other  case  it  is  the  formation  of  an 
insoluble  salt  of  an  acid. 

There  is  still  another  case  where  the  base  of  a  salt  is 
absorbed  and  the  acid  radicle  left  behind  as  an  acid.  There 
is  no  exchange  of  bases.  For  instance,  a  hydrated  silicate 
like  kaolinite  in  the  presence  of  a  salt  like  potassium  sulphate 
and  water  will  absorb  the  potassium,  probably  to  form  a 
potassium  silicate,  and  leave  sulphuric  acid.  This  applies 
to  salts  like  the  chlorides  and  sulphates  more  particularly. 


166  THE  SOIL:  INORGANIC  MATTER 

Other  things  being  equal  it  has  been  found  that  there  is  a 
difference  in  the  abihty  of  one  base  to  replace  another. 
Potassium  will  replace  magnesium  and  be  replaced  by 
ammonium  in  turn.  Sodium  will  replace  calcium  and  be 
replaced  by  magnesium.  In  other  words,  the  order  of 
replacing  power  beginning  with  the  strongest  is:  Ammo- 
nium, potassium,  magnesium,  sodium,  calcium.  Each  element 
will  replace  any  of  those  following  it  and  be  replaced  by  any 
of  those  preceding  it.  In  the  case  of  acid  radicals,  those 
which  form  insoluble  compounds  the  most  readily  are  the 
ones  absorbed  the  quickest.  •  Phosphates  of  calcium  (tri) 
and  of  iron  and  aluminium  are  insoluble.  Calcium  phosphate 
forms  soluble  acid  phosphates,  but  the  others  do  not  dissolve 
easily.  Carbonates  of  calcium  and  magnesium  are  insoluble, 
but  form  soluble  bicarbonates  very  readily.  Sulphates, 
except  of  barium,  are  rather  soluble.  Chlorides  and  nitrates, 
particularly  the  latter,  are  all  readily  soluble  and  hence  do 
not  form  compounds  which  can  be  retained  chemically. 

But  a  part  at  least  of  the  above  discussion  seems  to  be  at 
some  variance  with  what  has  been  said  in  Section  129  about 
the  solubility  of  soil  minerals.  The  fact  is  that  under  some 
conditions  elements  are  rendered  soluble  and  under  other 
conditions  the  same  elements  are  rendered  insoluble,  even 
when  the  reacting  substances  are  exactly  the  same,  and  this 
difference  of  reaction  depends  on  the  active  mass  of  the 
reacting  substances.    This  is  called  the  law  of  mass  action. 

133.  Mass  Action. — To  illustrate  this  important  chemical 
law,  the  equations  for  the  solution  of  phosphorus  and  for 
the  fixation  of  phosphorus  may  be  written  together  thus: 

Ca»(P04)2+  4C02+  4H2O  ^'~  CaH4(P04)2+  2CaH2(C03)8. 

This  is  called  a  reversible  reaction,  for  it  will  go  in  either 
direction  depending  on  the  active  mass  of  the  reacting  sub- 
stances. Tricalcium  phosphate  continues  to  go  into  solu- 
tion as  long  as  the  supply  of  carbon  dioxide  is  continuous, 
and  the  monocalcium  phosphate  or  calcium  bicarbonate  is 
removed  from  the  solution.  In  the  soil,  decomposition  of 
organic  matter  supplies  carbon  dioxide.    Growing  root  hairs 


PHYSICAL  ABSORPTION  167 

or  diffusion  may  remove  the  soluble  compounds.  The  re- 
action, then,  continues  to  go  from  left  to  right,  and  phos- 
phorus is  made  soluble. 

But  suppose  the  supply  of  carbon  dioxide  diminishes, 
because  organic  matter  for  some  reason  does  not  decompose 
very  rapidly  or  not  at  all;  or  suppose  no  plant  removes  the 
soluble  phosphate;  or  suppose  that  a  solution  of  monocal- 
cium  phosphate  passing  through  the  soil  comes  in  contact 
with  considerable  calcium  bicarbonate;  or,  more  than  all 
this,  suppose  fresh  supplies  of  calcium  bicarbonate  are  being 
continually  added  to  the  solution  from  other  places;  under 
these  conditions,  then,  the  reaction  goes  from  right  to  left 
and  phosphorus  is  absorbed  or  fixed  in  the  soil.  Of  course, 
in  all  cases  there  must  be  enough  water  present  to  allow  of 
reactions  in  solution. 

Starting  with  a  fixed  amount  of  the  reacting  substances 
the  reaction  will  proceed  in  a  direction  dependent  upon  the 
masses  until  an  equilibrium  is  reached,  or  until  the  masses 
on  one  side  of  the  equation  balance  in  reacting  velocity  those 
on  the  other  side.  This,  however,  is  something  that  rarely 
happens  in  a  soil,  for  the  composition  of  a  solution  is  con- 
stantly changing.  Reactions  in  a  soil  are  always  in  a  state 
of  change.     They  are  essentially  dynamic  and  not  static. 

This  reversible  reaction  and  the  resultant  solubility  or 
absorption  of  plant  food  is  applicable  just  as  well  in  the  case 
of  the  reactions  given  for  potassium  in  Sections  129,  b,  and 
132,  and  for  phosphorus  and  iron  compounds  in  Sections 
129,  a,  and  132. 

134.  Physical  Absorption. — Compounds  of  the  plant  food 
elements  are  retained  by  the  soil  to  a  greater  or  less  ex- 
tent in  an  unchanged  form.  Certain  solid  substances  in  the 
soil  attract  and  hold  on  their  surfaces  compounds  in  solu- 
tion. This  process  is  called  adsorption  and  may  be  defined 
as  that  property  of  a  solid  which  attracts  dissolved  substances 
and  causes  the  existence  in  such  solutions  as  soil  moisture 
of  two  different  concentrations  of  dissolved  substances,  the 
greater  lying  immediately  adjacent  to  the  surface  of  a  solid. 
For  example,  iron  and  aluminium  hydrated  oxides  have  a 
very  decided  affinity  for  potassium  sulphate.  Adsorption 
is  a  purely  physical  phenomenon  in  that  the  compounds 


168  THE  SOIL:  INORGANIC  MATTER 

held  are  not  chemically  changed.  They  remain  in  their 
original  form,  attached  to  the  surface  of  the  solid  as  by  a 
magnet,  and  the  amount  of  adsorption  depends  very  largely 
on  the  surface  exposed.  Hence,  the  smaller  the  soil  grains 
the  greater  the  adsorption  because  of  more  surface  exposed. 
Another  factor  in  adsorption  is  the  character  of  the  solids 
and  of  the  substances  in  solution.  Some  solids  have  greater 
attractive  powers  than  others,  and  some  dissolved  substances 
are  more  attracted  than  others.  For  example,  humus, 
hydrated  iron  and  aluminium  oxides,  and  hydrated  silicates 
or  so-called  zeolites,  have  greater  adsorptive  powers  than 
calcium  carbonate  and  quartz.  Potassium  salts  and  phos- 
phates are  attracted  more  than  sodium  salts  and  nitrates. 
Plant  foods  held  by  adsorption  on  the  surfaces  of  solids  are 
available  to  plants  if  the  root  hairs  come  in  contact  with 
them.  Substances  absorbed  chemically  are  not  available 
to  plants  until  they  are  dissolved  again,  as  may  or  may 
not  happen.  It  must  be  understood,  however,  that  in  no 
case  is  the  whole  of  a  substance  in  solution  absorbed  either 
chemically  or  physically.  No  chemical  reaction  is  complete 
in  the  soil.  Only  a  part  of  the  monocalcium  phosphate, 
for  example,  is  precipitated  as  iron  phosphate  at  any  one 
time,  but  enough  of  it  may  be  rendered  insoluble  to  affect 
the  growth  of  crops.    Moreover,  some  of  it  is  lost  by  leaching. 

135.  Movements  of  Dissolved  Substances. — Having  dis- 
cussed how  plant  foods  are  made  soluble  and  how  they  are 
retained  in  the  soil  after  being  made  soluble,  the  question 
naturally  arises  as  to  how  the  compounds  in  solution  move 
from  place  to  place.  That  plant  foods  do  move  is  obvious, 
for  they  are  lost  from  soils  in  the  drainage  water  and  eventu- 
ally are  deposited  in  the  ocean;  and  again  they  move  up- 
ward, for  incrustations  of  salts  which  have  been  lifted  by  the 
water  appear  on  the  surface  of  soils  in  arid  countries  (Sec- 
tion 138,  d). 

Movement  of  plant  food  in  the  soil  may  take  place  in  two 
ways :  First,  by  the  movement  of  water;  second,  by  diffusion. 

(a)  Movement  by  Water. — ^Water  moves  in  the  soil  in 
two  ways  to  aflFect  substances  in  solution,  by  gravity  and  by 
capillarity,  or  more  properly  by  surface  tension.  When  the 
saturation  point  of  soils  is  reached,  water  responds  to  the 


MOVEMENTS  OF  DISSOLVED  SUBSTANCES       1C9 

force  of  gravity  which  carries  it  downward  through  the  pore 
spaces  and  channels  in  the  soil.  This  bodily  movement  of 
water  carries  with  it  the  substances  in  solution  which  are 
not  absorbed  as  they  go.  The  water  may  go  directly  down 
in  a  vertical  direction  or  more  nearly  horizontally  if  any- 
thing like  an  impervious  subsoil  or  entrapped  air  deflects 
its  course.  Gravitational  movements  cease  as  soon  as  the 
excess  water  drains  off  and  the  surface  tension  overcomes  the 
force  of  gravity.  It  is  by  this  movement  that  soils  lose  plant 
foods  which  are  not  absorbed. 

The  surface  of  a  liquid  acts  as  if  it  exerted  at  all  times  a 
certain  tension  or  pressure  on  the  liquid  below.  If  a  drop 
of  liquid  is  free  to  take  any  position,  it  assumes  the  spherical 
form  in  which  the  surface  tension  is  uniform  throughout, 
that  is,  it  is  in  equilibrium.  When  the  surface  of  a  liquid 
is  forced  to  assume  various  shapes,  as  in  the  case  of  film 
water  covering  soil  particles,  there  is  exerted  an  unequal 
tension.  The  more  curved  the  surface  the  greater  the 
tension.  In  a  soil  the  surfaces  at  the  top  are  more  curved 
than  they  are  lower  down  where  the  films  are  thicker.  This 
means  that  the  pull  of  the  surface  tension  at  the  top  will 
tend  to  raise  water  until  the  gravity  pull  balances  the  ten- 
sion pull.  As  water  evaporates,  or  plant  roots  absorb  it, 
the  increasing  tension  caused  by  thinner  films  and  consequent 
greater  curvatures,  draws  up  more  water.  This  movement 
of  water,  of  course,  carries  with  it  dissolved  plant  food. 
Theoretically  this  movement  can  take  place  in  any  direction 
and  does  so  under  some  circumstances,  but  under  ordinary 
circumstances  the  increasing  surface  tension  occurs  on  top 
of  the  soil  because  of  evaporation,  and  hence  the  water 
movement  is  upward. 

(6)  Movement  by  Diffusion. — It  is  a  property  of  sub- 
stances, or  rather  of  the  molecules  of  such  substances  in 
solution,  to  move  within  the  solvent  from  a  region  of  greater 
concentration  to  one  of  less  concentration  in  that  particular 
compound.  That  is,  sodium  nitrate,  for  example,  tends  to 
move  from  that  portion  of  the  soil  moisture  where  its  con- 
centration is  considerable  to  other  portions  where  there  is 
little  or  no  sodium  nitrate.     This  movement  is  called  diffu- 


170  THE  SOIL:  INORGANIC  MATTER 

sion,  and  may  take  place  in  any  direction.  Within  the  soil 
liquid,  however,  there  is  opposed  to  diffusion  absorption 
both  chemical  and  physical.  Moreover  the  bodily  move- 
ment of  water  caused  by  gravity  or  by  surface  tension 
neutralizes  the  effect  of  diffusion  in  many  cases. 

As  a  matter  of  fact  diffusion  in  soils  does  not  play  a  very 
important  part.  Movements  of  plant  foods  in  solution  take 
place  for  the  most  part  in  a  general  direction  up  and  down; 
up  by  surface  tension,  down  by  gravity,  and  are  caused  by 
bodily  movements  of  water  containing  the  plant  foods. 
Experiments  have  repeatedly  demonstrated  that  plant  foods 
in  the  form  of  soluble  fertilizers  show  no  effect  laterally 
within  a  very  short  distance  from  the  point  of  application. 
That  is,  the  plant  foods  apparently  get  no  chance  to  diffuse, 
for  if  they  did  the  diffusion  would  be  in  every  direction  away 
from  the  point  of  application  and  the  effect  would  be  shown 
laterally  from  the  fertilizers. 

136.  Composition  of  Soil  Water. — ^From  the  preceding 
sections  it  has  been  seen  what  compounds  exist  in  a  soluble 
form  in  the  soil  moisture;  how  they  may  be  soluble  part  of 
the  time  and  insoluble  part  of  the  time  because  of  chemical 
change.  The  conditions  affecting  these  various  changes 
have  been  studied.  In  addition  to  this  information  it  may 
be  interesting  to  know  how  much  soluble  plant  food  material 
there  is  in  soils.  Soil  water  which  contains  the  soluble 
compounds  may  be  divided  into  two  classes  for  convenience 
of  study:   Film  water  and  drainage  water. 

(a)  Film  Water  is  the  liquid  in  the  soil  which  surrounds 
the  soil  grains  with  a  thin  film,  and  which  furnishes  plants 
with  their  foods.  It  bathes  the  plant  roots  with  their  nutrient 
fluid.  Determining  the  amount  of  soluble  material  in  this 
film  water  is  a  matter  of  great  diflSculty,  and  the  results  so 
far  obtained  can  be  considered  only  as  roughly  approximate, 
and  even  then  represent  but  a  few  soils.  However,  it  can  be 
said  that  the  following  figures  show  the  parts  per  million  in 
a  solution  that  probably  is  not  far  from  an  average  soil 
solution : 

N2O6  PjOs  '     KK)  CaO 

3  6  33  33 


COMPOSITION  OF  SOIL  WATER 


171 


These  figures  have  been  calculated  from  data  published 
by  the  Bureau  of  Soils.  They  show  that  at  any  one  time 
phosphorous  compounds  and  nitrates  are  present  in  con- 
siderably less  quantity  than  are  potash  and  lime.  It  is  true 
that  these  two  elements,  nitrogen  and  phosphorus,  are  usually 
the  limiting  essential  elements  in  crop  production,  as  this 


Fig,  38. — Waste  water.    Outlet  of  drain  tile.     (Elliott.) 


might  indicate;  but  on  the  other  hand,  if  these  concentra- 
tions are  maintained  throughout  the  growing  season  there 
will  be  enough  of  these  foods  supplied  to  nourish  the  crop. 
It  is  not  at  all  probable  that  this  same  concentration  is 
maintained  in  all  soils  and  at  all  times.  In  fact  quite  the 
contrary.    The  amount  of  material  in  the  film  water  must 


172 


THE  SOIL:  INORGANIC  MATTER 


vary  from  day  to  day  and  from  soil  to  soil,  depending  on 
daily  temperature  and  moisture  content,  soil  composition, 
texture  and  structure,  amount  of  organic  matter,  character 
of  the  solvent,  whether  rich  or  poor  in  carbon  dioxide  and 
organic  acids.  The  figures  given,  however,  show  only  what 
have  been  obtained  by  very  laborious  methods  from  a  few 
soils,  and  give  an  idea  of  the  amount  of  concentration. 

(b)  Waste  Water  is  the  excess  water  which  flows  away 
from  the  soil  as  drainage  or  river  water.  Table  IX  gives 
average  analyses  of  these  two  kinds  of  waste  water.  Drain- 
age water  is  that  which  has  been  obtained  from  drains  under 
cropped  fields  and  represents  that  which  comes  directly  from 
the  soil  after  having  passed  through  the  soil  and  subsoil 
(Fig.  38).  River  water  is  that  which  flows  into  the  sea 
and  has  travelled  for  long  distances  from  its  sources,  being 
subjected  to  many  changes  after'  passing  through  the  soil. 


Table  IX. — Composition  of  Drainage  and  River  Waters. 
Expressed  in  parts  per  million. 
(Averages  of  numerous  analyses  except  N2O6  in  the  ease  of  drainage  water, 
which  is  from  Rothamsted  figures.    There  are  not  many  analyses 
on  this  constituent.) 

Potash 
Soda     . 
Lime 
Magnesia 
Silica     . 
Carbon  dioxide 
Phosphoric  acid 
Sulphuric  acid 
Chlorine     . 
Organic  matter 
Nitric  acid 
Total  solids 


Drainage. 

Rivers. 

K20 

3.2 

2.4 

NaaO 

15.1 

7.1 

CaO 

.107.6 

43.2 

MgO 

16.3 

14.7 

Si02 

8.5  • 

16.4 

CO2 

74.4 

46.0 

P2O6 

0.5 

0.3 

S0» 

60.8 

8.0 

CI 

17.7 

3.7 

37.4 

16.4 

N2b6 

15.0 

3.8 

352.6 

168.6 

Since  the  figures  given  for  film  water  do  not  represent  as 
many  types  of  soil  as  those  in  Table  IX,  comparison  between 
them  is  hardly  proper.  Contrasting  drainage  water  with 
river  water  it  is  to  be  noted  that  in  practically  every  case 
the  latter  contains  less  of  the  various  constituents.  This  is, 
of  course,  to  be  expected,  for  after  the  drainage  water  has 
entered  an  open  stream  and  travelled  considerable  distances 


COMPOSITION  OF  SOIL  WATER  173 

much  of  the  soluble  material  is  deposited.  Aeration,  for 
example,  frees  carbon  dioxide  from  the  solution  and  pre- 
cipitates calcium  carbonate  and  magnesium  carbonate. 
Inter-reactions  of  bases  and  acids  with  new  compounds 
remove  many  substances.  Dilution  of  water  charged  with 
soluble  material  by  fairly  pure  water  reduces  the  con- 
centration. 

Taking  up  drainage  water  alone,  it  is  very  noticeable 
that  potash  is  present  in  small  quantities,  whereas  lime  is 
present  in  considerable  amounts;  and  it  will  be  remembered 
(Section  132)  that  potassium  is  absorbed  to  a  much  greater 
extent  than  calcium.  Soda  and  magnesia  are  present  in 
nearly  equal  quantities.  The  acid  radicles  in  the  order  of 
increasing  amounts  are  P2O5,  Si02,  CI,  SO3,  and  CO2,  with 
N2O5  probably  about  equal  to  CI.  Nitric  acid,  as  nitrates, 
of  course,  will  be  present  in  widely  varying  amounts,  probably 
more  widely  than  any  other  radical,  acid  or  basic,  and 
hence  an  average  figure  does  not  mean  much.  This  arrange- 
ment indicates  that  most  of  the  salts  in  solution  are  calcium 
and  magnesium  bicarbonates  and  sulphates,  sodium  chloride, 
some  silicates  of  the  alkalies,  and  nitrates  of  different  bases. 

It  may  be  said  for  nitrates  that  although  the  nitric  acid 
radical  is  the  least  absorbed  of  all,  there  is  not  such  a  great 
loss  of  it  from  ordinary  soils  as  might  be  expected.  Rapid 
growth  of  crops  at  the  time  when  nitrates  are  formed  in 
greatest  amount,  and  lack  of  moisture  for  nitrification  later 
in  the  season  when  crop  growi;h  practically  ceases,  are  two 
factors  which  tend  to  prevent  loss  of  nitrates.  The  practice 
of  fallowing,  w^hich  fortunately  is  not  very  common  nowa- 
days, always  results  in  a  heavy  loss  of  nitrates.  Conditions 
are  ideal  for  nitrification  and  there  are  no  crops  to  remove 
the  nitrates. 

Bicarbonates  and  sulphates  of  calcium  and  magnesium, 
present  in  largest  amounts  in  drainage  water,  are  what 
ordinarily  make  water  "hard,"  although  any  soluble  sub- 
stance may  be  responsible  for  this  condition.  The  hardness 
of  the  water-  depends,  of  course,  on  the  nature  of  the  soil 
drained.  A  limestone  country  yields  a  very  hard  water. 
The  bicarbonates  of  calcium  and  magnesium  give  a  water 


174  THE  SOIL:  INORGANIC  MATTER 

"temporary"  hardness,  because  they  decompose  easily  on 
aeration  or  boiling  and  precipitate  the  carbonates.  The 
sulphates  of  calcium  and  magnesium  give  water  "permanent" 
hardness,  since  they  are  not  so  easily  precipitated. 

Of  course  in  the  case  of  drainage  and  river  waters  there  is 
a  very  wide  variation  in  the  content  of  dissolved  material, 
just  as  there  is  in  the  film  water.  A  granitic  or  sandy  country 
will  yield  water  that  is  very  "soft"  or  almost  pure,  whereas 
a  limestone  country  gives  just  the  opposite.  Take  two 
fresh  water  lakes  in  Wisconsin,  for  example.  One — Devil's 
Lake — receives  the  drainage  from  a  granitic  region,  the 
other — Lake  Mendota — receives  that  from  a  limestone 
country.    Table  X  gives  the  analyses  of  both  lakes. 

Table  X. — Composition  of  Lakes. 
(Expressed  in.  parts  per  million.) 


SiO, 

Fe,0. 
AlsO, 

CaO    MgO 

SO, 

CI 

Lake  Mendota 

.      .       1.1 

0.8 

40.1     42.3 

10.3 

2.0 

Devil's  Lake    .      .      .      . 

.      .       2.2 

0.6 

4.5       1.8 

6.7 

8.2 

137.  Soil-forming  Rocks.  —  To  obtain  some  idea  of  the 
composition  of  a  soil,  it  is  necessary  to  know  something  of 
the  rocks  from  which  the  soil  is  derived.  Rocks  are  mineral 
aggregates,  that  is,  they  are  composed  of  two  or  more  minerals 
welded  together  either  by  heat  or  pressure.  They  are  classi- 
fied as  igneous,  formed  by  the  cooling  of  molten  masses; 
sedimentary,  laid  down  by  water;  and  metamorphic,  changed 
by  heat  and  pressure  from  their  original  forms.  Knowing 
the  rocks  in  a  general  way  will  give  an  idea  of  the  minerals 
to  be  expected  in  a  soil  derived  from  any  given  rock,  and  also 
the  character  of  the  compounds  resulting  therefrom.  This 
applies,  of  course,  only  to  soils  in  place.  Soils  that  have  been 
transported  by  water  have  been  sorted  more  or  less  accord- 
ing to  the  specific  gravity  of  their  various  constituents  and 
therefore  do  not  contain  all  of  their  original  minerals.  It  is 
impossible  to  describe  all  of  the  rocks  or  even  the  common 
rocks  from  which  soils  are  derived,  but  it  may  suffice  to 
mention  a  few  characteristic  soil-forming  rocks, 


SOIL-FORMING  ROCKS 


175 


(a)  Granite. — (Fig.  39).  This  is  one  of  the  most  common 
igneous  rocks  and  many  soils  are  derived  from  it.  It  is 
usually  composed  of  quartz,  feldspar,  mica,  and  hornblende. 


Fig.  39. — Soil-forming  rock:     Granite.     United  States  Geological  Survey. 


The  action  of  water,  heat,  and  cold  serve  to  break  it  down 
into  small  particles.  Aided  by  the  chemical  action  of  water 
and  carbon  dioxide  the  feldspar  changes  in  part  to  kaolinite 


176  THE  SOIL:  INORGANIC  MATTER 

and  silica,  or  clay  and  potassium  carbonate.  Mica  slowly 
changes  to  clay  and  carbonates  of  the  alkalies.  Hornblende 
forms  hydrated  oxides  of  iron  and  aluminium,  clay,  and 
carbonates  of  calcium  and  magnesium.  Quartz  changes 
but  little  except  as  to  size  of  particles,  these  becoming 
small  grains  which  form  sand. 

If  the  decomposed  material  is  not  disturbed  it  forms  a  soil 
of  excellent  texture  and  good  composition.  Apatite  occurs 
very  commonly  disseminated  in  small  crystals  throughout 
granite,  and  supplies  phosphorus  to  such  a  soil.  All  the 
other  essential  elements  are  present.  Sorted  by  water, 
however,  it  separates  into  sand  and  clay  soils  with  most  of 
the  plant  foods  in  the  clay. 

(b)  Basalts  and  Lavas  form  soils  which  may  be  very 
sandy  and  barren,  when  silica  predominates  with  only  cal- 
cium, magnesium,  and  aluminium  for  bases;  or  form  good 
soils,  when  bases  predominate,  which  include  potassium. 

(c)  Limestone  Rocks  consist  for  the  most  part  of  calcium 
carbonate  (and  magnesium  carbonate)  which  is  leached  out 
very  completely  by  the  action  of  water  and  carbon  dioxide 
(Fig.  40).  There  is  left  to  form  soil  only  a  very  small  per- 
centage of  impurities  in  the  form  of  clay.  Limestone  is 
laid  down  far  out  at  sea  in  deep  water,  and  there  is  entangled 
with  it  the  finer  and  lighter  particles  of  clay  which  have 
been  washed  out  into  the  sea  by  rivers.  This  clayey  im- 
purity which  forms  soil  from  limestone  may  have  been 
derived  from  granite,  in  which  case  it  would  be  fairly  rich 
in  plant  food.  It  may  have  been  derived  from  barren 
basalts,  in  which  case  it  would  be  very  poor.  As  a  rule, 
however,  limestone  soils  are  rich,  except  that  they  may  be 
lacking  in  calcium  carbonate.  At  first  thought  it  seems 
strange  that  limestone  soils  are  apt  to  be  lacking  in  calcium 
carbonate.  But  soil  is  derived  from  limestone  only  by  the 
solution  and  removal  of  calcium  carbonate,  soil  material 
being  only  the  impurities  present  in  the  limestone  rock. 
Calcium  carbonate  is  on  the  whole  very  soluble  in  soil  water, 
compared  to  other  rock  constituents.  Moreover,  the  particles 
composing  the  clay  are  for  the  most  part  decomposition 
products  of  silicates  which  may  have  originally  contained 


KINDS  OF  SOIL 


177 


calcium,  but  which  have  lost  a  large  part  of  this  constituent 
during  decomposition. 

Of  course,  there  may  be  particles  of  limestone  and  calcium- 
containing  silicates  left  in  the  soil,  and  these  serve  as  sources 
of  calcium  for  a  time,  but  nevertheless,  limestone  soils  are 
among  the  first  to  become  acid,  because  of  lack  of  calcium 
carbonate. 


■ 

W^^ 

^^^^^B^bp^^^^I 

^^^^^^^HB^ 

;^^^HB^I 

wKl^ 

'iK>.'  j^k 

ftflSli^B^^I^^I 

•■''-'' ■^J'ti 

^^K  vflj^H 

I^^^^H^^^H 

^^S^^T^ 

^^^^^^^^^^^^^^^^^9^^^^^^^^^l 

l^^^^^^^iH^^^^^^I 

■B^^  -*  -^w^  ■ 

■■' 

^^^^^^^^^^E^^^^^H 

W^^ 

^^^^^^^^H 

W^^Hmsm 

SBBeA     jL' 

^^^^^^^^^^^^^^^^B^B 

fk^^MKk 

hEw^m 

^^^^^^^Hj^^^Sj 

hB 

HHHj 

Fig.  40. — Soil-forming  rock:  Limestone.     United  States  Geological 
Survey. 


(d)  Sandstones  and  Shales  form  sandy  and  clayey  soils, 
respectively,  containing  more  or  less  plant  food  according 
to  their  original  composition  and  derivation,  for  they  are 
secondary  rocks  derived  from  decomposition  products  of 
others.  Sandstones  are  more  apt  to  yield  poor  soils  unless 
it  happens  that  the  binding  material  is  of  a  clayey 
nature. 

138.    Kinds  of  Soil. — The  number  of  different  kinds  of 

soil  is  necessarily  very  great,  and  any  attempt  to  classify 

them  is  a  very  considerable  undertaking.    Ordinarily  they 

are  divided  according  to  their  geological  origin,  but  they  may 

12 


178  THE  SOIL:  INORGANIC  MATTER 

be  classified  on  the  basis  of  physical  composition  or  of 
chemical  composition.  It  is  not  the  place  here  to  discuss 
soil  types  and  characteristics  in  detail,  but  it  may  be  of  some 
help  to  briefly  discuss  general  soil  classifications,  using  as  a 
basis  merely  the  common  terms  which  are  familiar  to  every 
farmer,  and  not  trying  to  adhere  rigidly  to  some  technical 
basis  which  is  of  value  only  to  the  soil  expert.  The  chemical 
properties  of  soils  in  every  case  will  form  the  basis  of  the 
discussion.  They  can  be  discussed  as:  (a)  Arid  and  humid 
soils,  which  will  distinguish  in  a  general  way  those  soils 
which  are  located,  on  the  one  hand,  where  very  little  rain 
falls,  and  on  the  other  hand,  where  sufficient  rain  falls; 
(6)  sand,  clay,  loam,  muck,  and  peat,  names  which  are 
very  commonly  used  and  which  depend  on  physical  and 
chemical  characteristics;  (c)  soil  and  subsoil,  terms  suffi- 
ciently plain;  (d)  alkali  soils  or  special  soils  that  are  very 
important  in  certain  arid  regions  of  the  United  States 
particularly — an  extreme  type  of  arid  soil. 

(a)  Arid  and  Humid  Soils. — The  principal  chemical  dif- 
ferences between  soils  in  an  arid  or  dry  region  and  those  in 
a  humid  or  moist  region  is  in  the  amount  of  available  or 
soluble  plant  food.  In  a  humid  climate  the  soil  is  continu- 
ally subject  to  leaching  and  fixation  of  soluble  compounds. 
Decomposition  takes  place  as  indicated  in  Section  129. 
In  a  region  of  little  rain,  the  plant  food  made  soluble  by 
decomposition  remains  in  the  soil  for  the  most  part  as  such. 
Decomposition  of  rocks  takes  place  largely  by  the  action 
of  sudden  extremes  of  heat  and  cold,  and  not  to  a  very 
great  extent  by  the  solvent  action  of  soil  moisture.  As  a 
result  arid  soils  are  not  only  pulverulent  and  sandy  in 
texture,  but  the  soluble  compounds  which  are  formed  remain 
in  the  soil.  Little  clay  is  formed  from  feldspars,  because  of 
lack  of  water  for  hydration.  This  means  a  soil,  coarse  in 
texture,  as  mentioned  above.  In  other  words  kaolinization 
is  not  marked  in  arid  regions.  Since  there  is  little  leaching, 
calcium  carbonate  derived  from  limestone,  or  from  silicate 
rocks  by  slow  decomposition,  is  not  removed  from  the  soil 
and  exerts  its  flocculent  effect  on  what  little  clay  is  formed. 
Arid  soils  are  more  fertile  as  a  rule  than  humid  soils  if  water 


KINDS  OF  SOIL 


179 


can  be  supplied  and  maintained.  Fig.  41  shows  the  method 
of  supplying  water  to  such  soils.  The  lack  of  organic  matter 
is  a  serious  drawback  in  arid  soils,  for  it  is  easily  "burned 
out."  Decomposition  is  very  rapid,  for  the  pulverulent  soils 
are  naturally  well  aerated. 


j^-^^;*'( 


i^m^ 


Fig.  41. — Arid  soil  under  irrigation.    Sugar  beets. 


(6)  1.  Sand  Soils. — ^The  term  sand  is  based  on  size  of 
soil  particles  and  not  on  chemical  composition,  although 
from  the  nature  of  its  formation  there  is  usually  a  distinct 
chemical  composition.  Technically  a  sand  soil  consists  of 
any  coarse  material  whether  composed  of  pieces  of  lava, 
coral,  shell,  or  pure  quartz.  Since  in  humid  regions,  however, 
sands  are  derived  by  the  action  of  water  and  carbon  dioxide 
on  rocks  containing  quartz,  such  soils  are  composed  largely 
of  silica,  Si02,  since  this  is  the  least  soluble  of  any  of  the 
ordinary  minerals,  and  breaks  up  slowly  largely  by  physical 
agencies.  There  are  present  in  addition  pieces  of  feldspar, 
mica,  and  hornblende.  As  a  rule  sandy  soils  do  not  contain 
much  organic  matter  for  the  reason  given  above — they  are 
too  well  aerated.    Fig.  42  shows  the  effect  of  organic  matter 


180 


THE  SOIL:  INORGANIC  MATTER 


on  such  soils.  In  humid  regions  the  grains  are  rounded 
from  the  rolHng  caused  by  water  movements.  In  arid 
regions  the  grains  are  angular  and  of  any  sort  of  material, 
not  necessarily  of  silica. 


Fig.  42. 


-Sand  soil.     Organic  matter  applied  to  plat  on  the  left. 
Department,  Wisconsin  Station. 


Soils 


2.  Clay  Soils. — Like  the  term  sand,  clay  in  soil  nomen- 
clature refers  to  size  of  particles,  and  is  applied  to  soils,  or 
that  portion  of  soils,  having  the  very  finest  particles,  regard- 
less of  composition.  It  has  been  truly  said  that  clay  is  either 
rock  rot  or  rock  flour.  In  the  former  case,  and  that  is  the 
common  occurrence,  clay  is  derived  from  silicate  rocks  by  the 
decomposing  action  of  water  and  carbon  dioxide.  It  is  largely 
hydrated  aluminium  silicate.  In  the  latter  case  clay  is 
merely  very  finely  ground  rock  material  made  by  the  action 
of  glaciers,  for  example,  and  the  composition  will  depend 
on  the  kind  of  rock  ground  up. 

3.  Loam  Soils. — ^The  term  loam  does  not  mean  much 
scientifically,  but  popularly  it  is  a  term  applied  to  soils  of 
good  texture  and  well  supplied  with  organic  matter.  They 
are  sand  or  clay  loams  as  they  have  more  or  less  of  the 
qualifying  constituent.  Their  chemical  composition  is  very 
general  in  nature. 


KINDS  OF  SOIL  181 

4.  Peat  Soils. — ^These  are  composed  for  the  most  part  of 
organic  matter  but  little  decomposed  (Fig.  43).  The  tissue 
of  the  plants  of  which  they  are  composed  is  still  plainly  dis- 
tinguishable. Unless  these  soils  are  in  a  limestone  region 
decomposition  results  in  the  production  of  a  considerable 
degree  of  acidity.  The  mineral  matter  present  frequently 
amounts  to  no  more  than  10  or  15  per  cent. 


Fig.  43. — Peat  soil.     Soils  Department,  Wisconsin  Station. 

5.  Miick  Soils. — ^These  are  soils  containing  large  amounts 
of  organic  matter,  but  which  are  in  a  more  advanced  state 
of  decomposition  than  peats.  Plant  tissue  is  quite  indis- 
tinguishable and  there  is  very  much  more  mineral  matter 
present. 

6.  General  Composition. — ^Table  XI  gives  the  approximate 
composition  of  sand,  clay,  muck,  and  peat  soils  in  three 
principal  constituents,  nitrogen,  phosphoric  acid,  and  potash. 
The  figures,  while  not  applicable  in  every  case,  will  at  least 
give  an  idea  of  relative  differences  as  they  very  commonly 
occur.  The  weight  of  the  surface  eight  inches  of  sand  is 
taken  at  2,500,000  pounds,  of  clay  at  2,000,000,  of  muck 
at  1,000,000,  and  of  peat  at  350,000. 


Table  XI. — Composition  of  General  S 

5oiL  Ttpi 

:s. 

Soil. 

Per  cent.     Pounds 
N.           per  acre. 

Per  cent.     Pounds 
PjOi.         per  acre. 

Per  cent. 
K,0. 

Pounds 
j>er  acre 

Sand 
Clay 
Peat 
Muck 

.      .     0.05         1250 
.      .     0.15         3000 
.      .     2.50         8750 
.      .     0.30        3000 

0.01            250 
0.15         3000 
0.25           875 
0.30         3000 

1.5 
2.0 
0.5 
1.6 

37.500 

40,000 

1,750 

15,000 

182  THE  SOIL:  INORGANIC  MATTER 

(c)  Soil  and  Subsoil. — In  humid  regions  there  is  a  con- 
siderable difference  between  the  soil  and  the  subsoil.  The 
most  striking  contrast  is  in  the  amount  of  organic  matter. 
In  fact  a  common  way  of  distinguishing  between  them  is  to 
note  the  dividing  line  between  the  dark  soil  and  the  light 
subsoil.  It  is  frequently  very  sharply  defined.  This  means 
of  course  that  there  is  more  nitrogen  in  the  soil  than  in  the 
subsoil.  In  addition  there  is  found  ordinarily  more  phos- 
phoric acid  and  total  lime  in  the  soil  than  in  the  subsoil. 
There  is,  however,  less  potash,  ferric  and  aluminium  oxides, 
and  calcium  carbonate.  The  finer  clay  particles  are  washed 
down  into  the  subsoil,  which  results  in  subsoils  of  finer 
texture  than  soils.  This  fact  also  accounts  for  the  greater 
amount  of  potash,  ferric  and  aluminium  oxides,  and  calcium 
carbonate  in  the  subsoil,  since  these  constituents  are  more 
rapidly  weathered  on  the  surface  and  washed  into  the 
subsoil,  where  they  are  fixed.  In  the  soil  there  are  more 
bacteria  and  bacterial  food — organic  matter — consequently 
there  are  more  organic  acids  and  carbon  dioxide.  The  latter 
makes  a  stronger  reagent  of  soil  moisture  and  as  a  result 
greater  availability  of  plant  food.  Being  more  open  and 
porous  and  of  better  structure  than  subsoil,  the  soil  is  in  better 
physical  condition  for  crop  growth.  Aeration  being  better, 
all  compounds  are  in  a  higher  state  of  oxidation,  iron,  for 
example,  is  all  in  the  ferric  form.  This  is  not  always  the  case 
in  subsoils.  Iron  may  be  in  the  ferrous  form,  and  such 
compounds  as  ferrous  sulphate  which  may  be  derived  from 
the  imperfect  oxidation  of  iron  sulphide  or  pyrites,  are 
poisonous  to  plants.  It  very  often  happens  that  when  too 
much  subsoil  has  been  turned  up  in  plowing  the  crop  is 
very  poor.  This  may  be  due  to  ferrous  salts,  to  poor  structure 
— too  compact  and  badly  aerated — to  lack  of  organic  matter. 
This  latter  lack  reduces  the  rate  of  availability  of  plant 
foods. 

In  arid  regions  there  is  very  little  difference  between 
soil  and  subsoil.  Organic  matter  extends  to  considerable 
depths,  because  of  deep  root  penetration.  There  is  no  sharp, 
dividing  line.  The  structure  is  the  same  throughout,  lack 
of  water  causing  little  clay  formation,  and  the  soils  are 


KINDS  OF  SOIL 


183 


pulverulent  all  the  way  down.  Weathering  is  uniform  and 
production  of  water-soluble  material  is  uniform.  The  sub- 
soil will  raise  just  as  good  crops  as  the  soil.  In  many  places 
material  thrown  out  in  excavating  for  the  cellar  of  a  house 
makes  just  as  good  a  garden  as  the  top  soil. 

(d)  Alkali  Soils. — In  certain  parts  of  the  arid  west,  as 
well  as  of  other  arid  regions  of  the  world,  there  exist  patches 
of  so-called  alkali  soil  (Fig.  44).  They  are  usually  barren 
of  vegetation  and  are  covered  with  white  or  black  incrusta- 
tions of  soluble  salts.  The  white  salts  are  called  "white 
alkali"  and  the  black  salts   "black  alkali."     Chemically 


Fig.  44. — Alkali  soil,  showing  patches  of  white  alkali, 
ment,  California  Station. 


Agronomy  Dcpart- 


the  white  salts  are  not  alkaline  in  character  but  consist 
largely  of  sodium  chloride  and  sodium  sulphate  with  some 
chlorides  and  sulphates  of  calcium  and  magnesium.  "Black 
alkali"  is  composed  largely  of  sodium  carbonate,  the  solution 
of  which  dissolves  from  the  soil  through  which  it  has  passed 
some  of  the  humus,  thus  coloring  the  evaporated  salts  black. 
As  was  noticed  in  Section  138  (a),  the  soluble  salts  formed 
by  decomposition  of  the  minerals  are  not  leached  out  of  arid 
soils,  and  under  normal  conditions  are  spread  throughout 
the  soil  and  subsoil  in  amounts  not  at  all  injurious  to  plants; 
but  when  there  arise  conditions  which  permit  the  accumula- 


184  THE  SOIL:  INORGANIC  MATTER 

tion  of  a  large  quantity  of  soluble  salts  in  one  spot,  then  the 
"rise  of  alkali,"  as  it  is  called,  begins.  For  example,  steady 
drainage  of  soluble  salts  from  a  higher  region  to  a  lower, 
with  insufficient  water  to  completely  remove  the  salts  in  the 
drainage  water,  results  in  the  accumulation  of  salts  in  the 
lower  area.  Where  irrigation  is  practiced  and  there  is  used 
water  heavily  charged  with  salts,  but  not  enough  water  to 
remove  the  salts  into  the  country  drainage,  an  accumula- 
tion is  apt  to  occur.  And  where  excessive  amounts  of  water 
are  used  for  irrigation  in  lands  not  properly  provided  with 
underdrainage,  the  rising  water  table  dissolves  out  the  soluble 
salts  in  the  subsoil  and  brings  them  within  capillary  reach 
of  the  surface. 

In  any  case  the  salts  in  solution  in  the  soil  water  rise  to 
the  surface  by  capillarity  and  are  left  there  by  the  evaporation 
of  the  water.  A  rain  dissolves  them  and  carries  them  into 
the  soil  for  a  greater  or  less  distance  depending  on  the 
amount  of  rainfall,  and  they  return  to  the  surface  when 
surface  tension  is  again  established. 

Many  different  kinds  of  compounds  are  made  soluble  by 
the  decomposition  of  rocks,  but  in  passing  through  con- 
siderable portions  of  soil,  chemical  absorption  plays  an 
important  selective  part.  As  was  seen  in  Section  132, 
potassium  and  magnesium  are  retained  more  than  sodium 
and  calcium.  Phosphates  are  easily  retained  in  an  insoluble 
form,  carbonates,  sulphates,  chlorides  less  easily.  As  a 
result  it  is  to  be  expected  that  chlorides,  sulphates,  and 
carbonates  of  not  easily  fixed  bases  will  predominate  in 
alkali  soils,  and  the  chloride,  sulphate,  and  carbonate  of 
sodium,  sulphates  of  calcium  and  magnesium,  and  some 
chlorides  of  calcium  and  magnesium  prevail  in  such  soils. 

White  alkali  is  not  so  injurious  to  vegetation  as 
black  alkali,  sodium  sulphate  being  the  least  injurious,  but 
both  kinds  are  very  troublesome  to  farmers  in  some  arid 
regions.  In  addition  to  the  harmful  effects  on  crops,  black 
alkali  or  sodium  carbonate  has  the  puddling  effect  on  soils 
common  to  most  alkaline  solutions.  Limiting  strengths  of 
these  salts  in  sandy  loam  soil  for  cereals  have  been  found  to 
be  about  0.1  per  cent,  of  sodium  carbonate,  0.25  per  cent. 


REFERENCES  185 

for  sodium  chloride,  and  0.5  per  cent,  for  sodium  sulphate. 
On  clay  soils  this  tolerance  is  less.  Crops  vary  in  their 
ability  to  withstand  the  alkali,  alfalfa,  sugar  beets,  and 
radishes  being  better  able  to  withstand  it  than  the  grains 
and  celery. 

Methods  of  reclaiming  alkali  soils  are  for  the  most  part  a 
matter  of  rotation,  culture,  the  growing  of  resistant  crops, 
prevention  of  evaporation,  flooding,  and  underdrainage. 
Black  alkali  can  be  remedied  by  the  application  of  gypsum 
or  land  plaster.  This  reacts  with  the  sodium  carbonate  to 
form  calcium  carbonate  and  sodium  sulphate,  the  former 
harmless  and  the  latter  relatively  so. 

EXERCISES 

1.  What  is  the  chief  solvent?  How  is  it  made  iu  the  soil?  State  what 
four  reactions  of  this  solvent  you  consider  the  most  important.  Why? 
How  are  these  reactions  related  to  the  phenomenon  of  absorption? 

2.  Why  does  drainage  water  contain  less  PjOs  and  K2O  than  CaO  and  N  ? 

3.  State  three  reasons  why  a  clay  soil  usually  retains  more  soluble  plant 
food  than  a  sandy  soil. 

4.  State  all  the  reactions  that  you  have  studied  that  are  probably  revers- 
ible. Is  reversibility  the  rule  or  the  exception  in  plant  and  soil  reactions? 
For  the  accomplishment  of  how  many  reactions  are  enzymes  necessary? 

5.  Examine  the  formulae  and  solubility  of  tricalcium  phosphate,  dicalcium 
phosphate,  monccalcium  phosphate,  pure  limestone  and  calcium  bicarbo- 
nate.    What  general  rule  becomes  apparent? 

6.  Other  things  being  equal,  will  a  soil  in  which  much  kaolinization  has 
taken  place  permit  KCl  to  leach  away  as  readily  as  one  in  which  this  action 
has  not  taken  place?     Why  or  why  not? 

7.  What  are  the  two  chief  functions  of  carbon  dioxide  from  the  fanner's 
standpoint? 

8.  Suppose  you  added  equal  amounts  of  soluble  compounds  containing 
the  following  radicals  to  the  soil,  NOj,  NH4,  PO4,  Ca  and  K;  place  them 
in  an  order  that  shows  the  increasing  ability  to  leach. 

9.  Suppose  a  farmer  added  acid  phosphate  to  a  soil  that  was  very  poor 
in  organic  matter  but  rich  in  lime;  explain  in  detail  what  would  happen  to 
the  acid  phosphate. 

10.  From  what  kind  of  organic  matter  can  nitric  and  sulphuric  acid  be 
produced  in  the  soil? 

11.  Explain  in  detail  why  an  acid  soil  is  often  lacking  in  available  phos- 
phorus. 

12.  Explain  why  little  kaolinization  takes  place  in  an  arid  soil. 

13.  Why  are  soil  minerals  less  soluble  in  warm  water  containing  carbonic 
acid  than  in  cold  water  containing  this  solvent? 

REFERENCES 
See  references  at  end  of  Chapter  VI. 


CHAPTER  VIII 
FERTILIZERS 

It  frequently  happens  that  soils  lose  their  ability  to 
raise  good  crops.  They  no  longer  continue  to  produce  the 
high  yields  which  are  characteristic  of  soils  functioning 
properly  in  accordance  with  the  facts  stated  in  the  last  two 
chapters.  This  failure  may  be  due  to  several  causes:  Poor 
drainage,  insufficient  water,  bad  physical  condition,  not  enough 
organic  matter,  and  lack  of  available  plant  food.  MoSt  of  the 
conditions  can  be  remedied  by  the  farmer.  Insufficient  water 
cannot  be  prevented  except  by  irrigation  where  a  source 
of  water  is  convenient  and  it  is  possible  to  ditch  the  land. 
All  other  factors  can  be  modified.  In  this  discussion  of 
the  chemical  phase  of  soil  fertility  only  one  factor  can  be 
considered,  namely,  the  supply  of  plant  food,  available  or 
total. 

139.  Plant  Food  in  the  Soil. — ^When  it  is  a  question  of 
unavailable  plant  food,  attention  to  such  things  as  cultiva- 
tion and  the  supply  of  organic  matter  will  frequently  remedy 
the  deficiency;  but  where  these  factors  are  insufficient,  or 
where  plant  foods  are  actually  lacking,  then  it  becomes 
necessary  to  add  them  to  the  soil. 

From  Table  III,  p.  109,  showing  the  number  of  pounds  of 
nitrogen,  phosphoric  acid,  and  potash  removed  from  an  acre 
by  various  crops,  it  can  readily  be  seen  that  there  is  a  steady 
drain  on  the  reserve  food  supply  in  the  soil,  and  no  compensa- 
tive natural  return.  In  the  case  of  nitrogen  there  is  an  addi- 
tion of  possibly  40  to  60  pounds  of  nitrogen  in  the  roots  and 
stubble  of  one  legume  crop.  This  is  in  excess  of  the  amount 
removed  from  the  soil  and  illustrates  very  forcibly  the 
necessity  of  growing  a  legume  in  the  rotation.  And  yet, 
compared  to  the  total  amount  of  nitrogen  removed  in  the 
( 186 ) 


DEFINITION  OF  FERTILIZERS  187 

other  crops  of  a  rotation,  this  is  inadequate  to  make  up  the 
loss — 40  to  60  pounds  returned,  and  100  to  150  pounds 
removed. 

There  may  be  added  to  the  soil  of  one  field  more  or  less 
fine  soil  blown  from  an  adjoining  field  or  roadway.  This,  of 
course,  adds  some  plant  food  such  as  potash  and  phosphoric 
acid,  but  it  is  at  best  only  "robbing  Peter  to  pay  Paul,"  since 
this  plant  food  may  in  turn  be  lost  to  the  next  field  in  the  same 
way.  There  is,  of  course,  some  plant  food  brought  to  the 
surface  soil  by  the  rise  of  capillary  or  film  water,  and  the 
decay  of  roots  and  stubble  may  add  plant  food  which  has 
been  brought  up  from  the  subsoil  by  deeply  penetrating 
roots.  But  analyses  show  very  conclusively  that  a  long 
period  of  cropping  reduces  all  the  plant  food  elements.  As 
much  as  one-third  to  one-half  of  the  amount  contained  in  the 
virgin  soil  has  been  found  to  disappear  during  50  to  60 
years  of  cropping  with  no  return  in  the  way  of  manure  or 
fertilizers. 

It  is  a  well-recognized  fact  among  farmers  who  have  the 
experience  of  centuries  to  guide  them  that  if  plant  food  is 
removed  it  must  be  returned.  F.  H.  King  in  his  "  Farmers  of 
Forty  Centuries"  states  that  to  each  acre  of  the  20,000 
square  miles  of  cultivated  land  in  Japan  there  are  added 
annually  60  pounds  of  nitrogen,  32  pounds  of  phosphoric 
acid,  and  48  pounds  of  potash.  These  people  have  been 
farming  for  centuries  and  are  still  maintaining  the  fertility 
of  their  soil  only  by  a  most  rigorous  return  to  the  soil  of  the 
plant  food  removed. 

These  facts  all  show  that  sooner  or  later  plant  food  must 
be  added  to  the  soil. 

140.  Definition  of  Fertilizers. — The  term  fertilizer  is  ap- 
plied not  only  to  a  compound  which  supplies  a  plant  food 
to  the  soil,  but  also  to  a  compound  which  has  other  func- 
tions in  the  soil,  such  as  neutralizing  acidity,  making  potash 
available,  etc.  Hence,  fertilizers  maj^  be  defined  as  com- 
pounds which  are  added  to  the  soil  to  increase  the  yield  of 
crops — to  increase  the  fertility  of  the  soil. 

141.  Direct  Fertilizers. — Compounds  which  supply  plant 
food  to  the  soil  and  thus  have  a  direct  action  on  plant  growth 


188  FERTILIZERS 

are  called  direct  fertilizers,  and  are  usually  compounds 
containing  nitrogen,  phosphoric  acid,  or  potash  which  are 
the  three  elements  most  commonly  lacking  in  soils,  either 
because  of  low  total  content  like  nitrogen  and  phosphoric 
acid,  or  because  of  unavailability  like  potash.  The  addition 
of  the  other  essential  elements  is  rarely  necessary,  with  the 
exception  of  calcium. 

142.  Indirect  Fertilizers  or  Amendments.  —  Compounds 
which  are  not  added  primarily  to  supply  plant  food,  but 
which  cause  some  other  plant  food  to  become  available,  and 
which  correct  a  harmful  condition  in  the  soil,  or  act  as  a 
stimulant  to  plant  growth  by  other  causes  than  merely  nutri- 
tive, are  called  indirect  fertilizers  or  amendments.  Calcium 
in  various  forms  is  usually  called  an  indirect  fertilizer, 
although  as  noted  in  Chapter  XII,  calcium  may  frequently 
serve  as  a  plant  food.  Sodium  chloride,  manganese  salts,  and 
sulphur,  are  all  classed  as  indirect  fertilizers  or  amendments. 

143.  Commercial  Fertilizers. — Under  this  head  come  all 
those  fertilizers  which  the  farmer  buys — compounds  which 
are  of  great  commercial  importance.  Compounds  which  are 
produced  on  the  farm,  such  as  barnyard  manure  or  green- 
crop  manures,  are  not  rated  as  commercial  fertilizers. 

144.  Complete  Fertilizers. — A  complete  fertihzer  is  one 
which  contains  nitrogen,  phosphoric  acid,  and  potash. 
These  three  constituents  are  the  only  ones  which  the  farmer 
needs  to  consider  as  being  necessary  to  purchase  for  plant 
food.  Nitrogen  and  phosphoric  acid  exist  in  soils  in  very 
small  amounts  and  are  hence  very  likely  to  be  lacking  in 
sufficient  quantity  to  nourish  crops.  Potassium  on  the  other 
hand  is  rarely  lacking,  but  is  very  frequently  present  in  such 
unavailable  form  that  certain  plants  cannot  obtain  enough  for 
normal  growth.  Of  the  other  essential  elements,  none  is 
ever  actually  lacking  in  soil  for  the  nutrition  of  the  plant, 
except  calcium.  But  since  calcium  is  usually  referred  to  as 
a  soil  amendment  or  indirect  fertilizer,  discussion  of  this 
element  as  a  plant  food  will  be  postponed. 

In  preparing  a  complete  fertilizer  for  the  market  the 
manufacturer  makes  use  of  various  compounds  of  nitrogen, 
phosphoric  acid,  and  potash  in  forms  that  are  immediately 


HOME  MIXING  189 

soluble,  or  will  become  soluble  very  quickly.  The  farmer 
wants  quick  returns  from  his  fertilizer  and  hence  the  various 
ingredients  must  be  readily  available.  Chapters  IX,  X, 
and  XI  give  the  various  sources  of  the  individual  elements. 
An  almost  infinite  number  of  combinations  of  the  different 
constituents  can  be  made  and  the  manufacturer  uses  many 
of  them,  with  phosphoric  acid,  however,  predominating 
in  most  of  the  fertilizers.  In  making  the  so-called  high 
grade  fertilizers  only  compounds  containing  the  maximum 
amount  of  nitrogen,  phosphoric  acid,  and  potash  are  used,  but 
even  here  it  is  not  possible  to  manufacture  a  product  contain- 
ing very  much  of  the  essential  elements.  Few  nitrogenous 
materials  contain  more  than  15  per  cent,  nitrogen,  or  phos- 
phate substances  more  than  16  to  18  per  cent,  available 
phosphoric  acid,  or  potash  compounds  more  than  50  per  cent, 
potash.  The  rest  of  the  product  is  worthless  as  a  fertilizer, 
but  its  presence  can  not  be  helped,  for  it  is  obviously  impos- 
sible to  use  elemental  nitrogen,  or  phosphorus  pentoxide,  or 
potassium  oxide  in  a  fertilizer  (cf.  Section  198).  In  making 
low  grade  fertilizers,  however,  various  diluents  are  used  to 
reduce  the  percentage  composition;  diluents,  however, 
which  are  harmless  in  themselves,  although  of  course  value- 
less as  fertilizers.  These  substances  are  gypsum,  fine,  dry 
soil,  peat  (which  does  contain  a  small  amount  of  nitrogen, 
although  not  very  available),  sawdust,  and  other  dry,  cheap 
substances.  Sometimes  it  is  necessary  to  add  these  materials 
to  a  complete  fertilizer  to  serve  as  driers,  for  some  single 
fertilizer  ingredients,  like  sodium  nitrate,  absorb  water  and 
make  the  mass  sticky,  or  cause  it  to  cake  in  hard  lumps  and 
hence  render  it  unfit  for  drilling  purposes. 

145.  Incomplete  Fertilizers. — An  incomplete  fertilizer  is 
one  which  contains  only  one  or  two  of  the  above  named 
three  elements.  Those  containing  only  one  aire  frequently 
referred  to  as  single  fertilizers. 

146.  Home  Miaring. — It  is  not  necessary  for  the  farmer 
to  purchase  ready  mixed  goods.  He  may  buy  single  ferti- 
lizers and  do  his  own  mixing  before  application,  or  he  may 
apply  them  singly  to  the  soil.  Each  purchaser  should  decide 
for  himself  which  wav  is  the  best  for  him.     There  are 


190  FERTILIZERS 

advantages  and  disadvantages  in  the  use  of  either  form. 
Ready  mixed,  complete  fertilizers  are  easily  purchased  in 
any  quantity,  with  a  wide  variety  of  combinations  in  nitrogen, 
phosphoric  acid,  and  potash,  and  in  a  fine,  dry  condition 
which  will  run  readily  through  a  fertilizer  drill.  The  mixture 
is  uniform  throughout.  On  the  other  hand,  they  are  expensive 
and  the  farmer  does  not  know  what  the  various  ingredients 
are.  Particularly  in  the  case  of  nitrogen,  the  farmer  does 
not  know  the  source.  It  may  be  readily  available  and  it 
may  not,  although  in  a  majority  of  cases  it  is  in  a  reasonably 
soluble  form. 

Home  mixed  goods  are  cheaper,  the  farmer  knows  the 
source  of  his  materials,  and  he  can  apply  one  element  at  a 
time  or  only  those  which  are  necessary,  without  adding  plant 
food  which  is  not  needed  in  order  to  get  that  which  is  re- 
quired. On  the  other  hand,  it  is  not  always  easy  to  get  small 
amounts  of  the  separate  ingredients — and  this  is  because 
the  manufacturer  prefers  to  sell  the  single  ingredients  in 
mixed  form  if  possible.  Again,  it  is  not  always  easy  to  get 
a  uniform  mixture  and  this  may  result  in  uneven  yields. 
Finally  the  mechanical  condition  may  be  such  that  the 
material  can  not  be  drilled,  and  even  if  used  otherwise  it 
must  be  broken  up  before  use.  This  is  due  to  absorption  of 
moisture  as  above  indicated. 

147.  Mixtures  to  be  Avoided. — In  mixing  fertilizers  care 
must  be  taken  not  to  put  together  two  or  more  substances 
which  will  cause  loss  of  plant  food  or  conversion  to  an 
insoluble  form.  Lime  in  any  form,  or  basic  slag  which 
contains  an  excess  of  lime,  or  wood  ashes,  should  not  be 
mixed  with  ammonium  sulphate,  or  with  organic  nitrog- 
enous materials,  for  loss  of  ammonia  would  occur.  The 
same  compounds  should  not  be  mixed  with  acid  phosphate 
because  reversion  to  the  insoluble  form  takes  place  and  the 
fertilizer  loses  its  immediate  value. 

Unless  a  mixture  is  to  be  used  at  once  it  is  better  not  to 
mix  the  basic  compounds  named  above  with  sodium  nitrate 
or  with  potash  salts,  for  the  latter  absorb  moisture  and  the 
whole  mass  will  harden  to  a  solid  mass  which  requires 
crushing  before  use. 


REFERENCES  191 

148.  Choice  of  Fertilizers. — In  the  following  discussion  of 
various  fertilizers  there  are  considered  for  the  most  part 
only  their  effects  on  the  plant,  the  soil,  and  on  each  other. 
Their  relative  value  as  forms  of  plant  food  is  considered 
only  on  these  grounds.  But  it  must  be  remembered  by  the 
farmer  that  the  economical  factor  should  enter  into  the  choice 
of  a  fertilizer.  As  a  matter  of  scientific  fact  one  form  of 
fertilizer  may  be  better  than  another,  but  its  cost  may  be 
greater  than  the  increased  benefits  derived  from  its  use. 
With  a  thorough  knowledge  of  the  several  forms  of  each 
element,  of  the  effects  of  each  crop  to  be  grown,  of  the 
soil,  and  of  the  cost,  a  farmer  can  decide  for  himself  which 
is  the  best  kind  to  use  under  the  circumstances. 

EXERCISES 

1.  Give  as  many  reasons  as  you  can  why  substances  containing  Ca,  N,  P, 
and  K  are  the  important  fertilizers. 

2.  Would  it  be  wise  to  mix  the  following:  Sodium  nitrate  with  lime; 
ammonium  sulphate  with  potassium  chloride;  lime  with  monocalcium 
phosphate?  If  not,  why  not?  How  many  mixtures  to  be  avoided  can  you 
give? 

3.  Would  it  be  harmful  to  mix  lime  with  ammonium  sulphate  in  the  soil? 
Why  or  why  not? 

4.  What  condition  of  a  crop  would  indicate  the  need  of  a  nitrogenous 
fertilizer;  of  a  phosphatic  ferlilizer;  of  a  potash  fertilizer? 

5.  What  kind  of  a  fertilizer  would  you  think  most  valuable  for  potatoes; 
corn;  cabbage;  sugar  beets;  to  mature  a  crop  early;  to  give  rapid  vegetative 
growth?     Why? 

6.  What  properties  sljould  a  fertilizer  have  in  order  to  be  immediately 
available;  to  be  used  as  a  spring  dressing;  to  have  residual  effects? 

7.  A  firm  advertises  a  brand  of  rock  phosphate  containing  13  per  cent. 
P  at  $30  per  ton.  Another  firm  sells  the  same  kind  of  fertilizer  under  a 
different  trade  name,  and  guaranteed  to  contain  32  per  cent.  PjOs,  for  S31 
per  ton.  Which  fertilizer  will  give  the  greater  amount  of  P  for  SIO,  and 
how  much  more  than  the  other? 


REFERENCES 

Hall.     Fertilisers  and  Manures. 
Halligan.     Soil  Fertility  and  Fertilizers. 
Pranke.     Cyanamid. 
Van  Slyke.     Fertilizers  and  Crops. 
Wheeler.     Manures  and  Fertilizers. 


CHAPTER  IX 
NITROGENOUS  FERTILIZERS 

Nitrogen  has  usually  been  considered  the  most  important 
element  in  plant  nutrition,  and  for  several  reasons:  It 
exists  in  the  soil  in  only  small  quantities,  rarely  more  than 
0.2  per  cent.  It  is  so  important  in  the  vegetative  growth  of 
plants  that  frequently  nitrogen  is  the  only  fertilizing  con- 
stituent needed  to  produce  large  yields.  In  other  words,  the 
increased  growth  of  leaves  and  stems  gives  the  plant  more 
power  to  forage  for  the  other  elements,  in  the  soil  and  so 
produce  a  greater  yield.  It  goes  for  the  most  part  to  the 
seed,  and  thus,  in  the  case  of  grain  crops,  is  one  of  the  ele- 
ments that  is  removed  from  the  soil.  It  is  used  by  plants 
to  a  greater  extent  than  any  other  element. 

As  a  matter  of  physiological  fact,  of  course,  no  one  element 
is  more  important  than  another.  All  the  essential  elements 
are  equally  necessary  for  the  growth  of  the  plant;  some  in 
larger  amounts  than  others,  it  is  true,  but  not  more  necessary. 
And  yet,  important  as  nitrogen  is  in  many  ways,  it  is  the 
only  element  which  can  be  returned  to  the  soil  by  natural 
means,  namely,  by  the  agency  of  nitrogen-fixing  bacteria  on 
the  roots  of  legumes  (Section  125).  Clover,  alfalfa,  or  some 
other  legume,  is  always  a  part  of  a  good  rotation  system. 
So  that  after  all,  nitrogen  is  not  the  important  element  for 
the  farmer  to  consider. 

In  taking  up  the  different  forms  of  nitrogen  on  the  market 
it  is  convenient  to  classify  them  according  to  the  form  of 
chemical  combination,  and  this  order  coincides  with  the 
solubility,  and  roughly  with  the  availability  of  the  nitrogen 
compounds. 
(192) 


NITROGEN  AS  NITRATE 


193 


I.    NITROGEN  AS  NITRATE 

149.  Sodium  Nitrate,  NaNOs. — The  best  known  and  most 
important  of  all  the  nitrogen  fertilizers  is  sodium  nitrate, 
or  more  commonly,  nitrate  of  soda,  or  "Chile  saltpeter." 
Saltpeter  itself  is  potassium  nitrate  which  is  too  expensive 
for  ordinary  use  as  a  fertilizer,  although  on  account  of  the 
fact  that  it  contains  both  potassium  and  nitrogen  it  is  a 
plant  food  of  great  value.  Nitrate  of  soda  is  a  salt  similar 
to  potassium  nitrate  in  many  of  its  properties,  and  because 
most  of  the  world's  supply  comes  from  Chile,  it  has  received 
the  name  of  Chile  saltpeter. 


Fig.  45. — Gathering  caliche. 

(a)  How  Obtained. — The  principal  deposit  of  nitrate  of 
soda  lies  on  a  plateau  some  3000  feet  above  sea-level  in  a 
region  where  rain  falls  but  once  in  two  or  three  years.  The 
crude  salt,  called  "caliche"  (Fig.  45),  is  found  in  masses  which 
average  about  3  feet  thick.  On  top  are  strata  of  gravel  and 
rock  several  feet  thick.  The  rock  is  composed  largely  of 
sand  and  gypsum,  while  the  caliche  contains  from  17  to  60 
per  cent,  sodium  nitrate  mixed  with  various  impurities  such 
as  sodium  chloride,  calcium,  magnesium,  and  sodium  sul- 
phates, some  iodates  and  perchlorates.  Dynamite  is  used 
13 


194  NITROGENOUS  FERTILIZERS 

to  loosen  up  the  masses  of  caliche  and  to  break  up  the 
overlying  strata.  From  the  mines  the  crude  material  is 
taken  to  the  works  where  it  is  dissolved  in  hot  water,  trans- 
ferred to  evaporating  tanks,  and  the  sodium  nitrate  allowed 
to  crystallize  out  (Fig.  46).  It  is  then  dried  and  sacked 
for  shipment.  As  it  comes  on  the  market  nitrate  of  soda 
is  coarsely  granular  material,  brown,  gray,  or  pink  in  color 
and  most  of  it  is  about  96  per  cent,  pure,  containing  in 
addition  to  sodium  nitrate,  some  moisture,  sodium  chloride, 
calcium,  magnesium,  and  sodium  sulphates.  The  nitrogen 
content  is  nearly  16  per  cent. 


Fig.  46. — Nitrate  of  soda  in  crystallizing  pans. 

(6)  Availability. — Since  nitrate  of  soda  is  very  soluble, 
one  part  dissolving  in  about  one  part  of  water,  and,  more- 
over, since  its  nitrogen  is  in  the  form  which  plants  require, 
it  is  an  immediately  available  fertilizer.  In  addition  to  its 
being  very  soluble  it  is  not  fixed  or  retained  by  the  soil 
to  any  extent,  and  is  therefore  easily  lost  by  leaching.  Con- 
sequently applications  of  sodium  nitrate  should  be  made  a 
very  short  time  before  seeding,  or  as  a  top  dressing. 

(c)  Effect  on  the  Soil. — In  the  soil  sodium  nitrate  serves 
as  an  indirect  fertilizer  in  that  it  reacts  with  insoluble  potas- 
sium compounds,  making  the  potassium  soluble.     Experi- 


NITROGEN  AS  NITRATE  195 

merits  have  shown  that  sodium  nitrate  in  this  way  takes 
the  place  of  a  potash  fertilizer,  in  addition  to  supplying 
nitrogen  to  the  crop.  Another  effect  of  sodium  nitrate  in 
the  soil  is  to  puddle  heavy  soils,  if  used  continuously.  This 
is  because  plants  absorb  more  of  the  nitrate  radical  than 
they  do  of  the  sodium.  The  latter  unites  with  carbon 
dioxide  in  the  soil  forming  sodium  carbonate  which  de- 
flocculates  clay  particles,  giving  the  soil  a  very  poor  structure. 
This  fact  of  its  leaving  a  residue  of  sodium  carbonate 
in  the  soil,  however,  makes  sodium  nitrate  a  valuable 
fertilizer  on  acid  soils,  and  thus  saves  the  calcium  carbonate 
by  supplying  an  additional  base. 

150.  Synthetic  Nitrates. — ^Years  ago  when  it  was  thought 
that  the  Chilean  nitrate  beds  were  in  serious  danger  of 
rapid  exhaustion,  attention  was  directed  to  methods  of 
combining  the  nitrogen  of  the  air  with  other  elements,  and 
so  to  ward  off  inevitable  destruction  when  no  more  nitrate 
was  to  be  procured.  Although  such  a  danger  was  very 
much  overrated  it  served  the  purpose  of  stimulating  inven- 
tion. More  recently  the  Great  War  demonstrated  the 
necessity  of  making  nitric  acid  from  air  nitrogen  for  explo- 
sives. As  a  result  Germany  was  able  to  make  in  this  way 
all  the  nitric  acid  necessary  for  military  as  well  as  for  agri- 
cultural purposes.  In  the  Allied  countries  much  was  also 
done  in  the  way  of  making  nitric  acid  from  the  nitrogen 
of  the  air.  In  the  United  States  several  plants  were  started 
but  at  present  little  is  being  done  to  operate  them.  They 
have,  however,  demonstrated  the  possibilities.  In  times  of 
peace  the  products  from  such  plants  can  be  used  largely 
for  fertilizers. 

How  Made. — It  has  been  known  for  over  a  century  that 
nitrogen  and  oxygen  would  unite  if  heated  to  a  sufficiently 
high  temperature,  as  by  an  electric  spark.  This  fact  is 
made  use  of  in  a  number  of  different  processes,  particularly 
that  of  Birkeland  and  Eyde  in  Norway.  The  union  of 
nitrogen  and  oxygen  is  brought  about  in  a  specially  con- 
structed furnace  (Figs.  47  and  48)  which  contains  a  large 
and  powerful  electric  arc  through  which  air  passes.  Oxides 
of  nitrogen  are  formed  which  later  are  combined  with  water 


196 


NITROGENOUS  FERTILIZERS 


to  produce  nitric  acid.     This  acid  can  be  neutralized  with 
lime  or  ammonia  for  fertilizer  purposes. 


Fig.  47. — Manufacture  of  calcium  nitrate.    Interior  view  of  furnace  house 
at  Notodden,  Norway. 


Fjg.  48. — Interior  of  one  of  the  furnaces  at  NotocJdeo. 


NITROGEN  AS  AMMONIA  197 

Another  method,  the  so-called  Haber  process,  synthesizes 
ammonia  from  pure  nitrogen  and  pure  hydrogen  under  great 
pressure,  at  a  moderate  temperature  and  in  the  presence  of 
a  catalyst.  The  ammonia  can  be  oxidized  to  nitric  acid 
by  being  passed  over  red  hot  platinum  gauze  with  an  excess 
of  air.  With  part  of  the  ammonia  oxidized  to  nitric  acid 
and  part  unchanged,  ammonium  nitrate  can  be  produced. 
This  compound  may  in  time  become  valuable  as  a  fertilizer, 
although  it  i^  not  used  to  any  extent  at  present. 

n.    NITROGEN  AS  AMMONIA 

151.  Ammonium  Sulphate. — In  addition  to  the  nitrate 
nitrogen  mined  as  nitrate  of  soda  and  manufactured  as 
nitrate  of  lime,  there  is  produced  an  ammonia  nitrogen 
fertilizer  called  ammonium  sulphate,  (NH4)2S04,  which 
contains  about  20  per  cent,  nitrogen  as  it  appears  on  the 
market.  Ammonium  sulphate  is  obtained  for  the  most 
part  as  a  by-product  in  the  destructive  distillation  of  soft 
coal.  Coal  contains  from  1  to  2  per  cent,  nitrogen,  of  which 
about  15  per  cent,  is  recoverable.  In  other  words,  from  one 
ton  of  coal  may  be  produced  about  twenty  pounds  of  am- 
monium sulphate.  For  years  none  of  this  valuable  material 
was  saved,  and  even  now  not  all  of  the  amount  produced  is 
recovered. 

(a)  How  Made. — If  soft  coal  is  burned  in  the  air  all  the 
nitrogen  escapes  as  elemental  nitrogen  and  cannot  be  re- 
covered, but  if  coal  is  heated  in  closed  retorts,  it  undergoes 
destructive  distillation  whereby  coke  and  Combustible  gases 
are  formed,  the  latter  containing  part  of  the  nitrogen  in  the 
form  of  ammonia.  Soft  coal  is  treated  in  this  way  in  the 
manufacture  of  coke,  coal  gas,  or  producer  gas,  and  in  any 
one  of  these  processes  it  is  possible  to  save  the  ammonia. 
The  coke  ovens  have  been  the  greatest  source  of  loss,  for  in 
the  past  no  attempt  was  made  to  save  any  of  the  gases, 
and  even  now  not  as  many  by-product  coke  ovens  are  in 
use  as  should  be,  although  the  coke  and  steel  concerns  are 
beginning  to  realize  the  advantage  of  saving  the  ammonia 
(Figs.  49  and  50). 


198 


NITROGENOUS  FERTILIZERS 


By  proper  appliances  the  escaping  gases  from  coke  ovens 
or  gas  retorts  are  led  through  water  in  which  the  ammonia 


Fig.  49 


Fig.  50 


Ah    4 


Figs.  49  and  50. — Two  views  of  by-product  coke  ovens. 


NITROGEN  AS  AMMONIA  199 

is  dissolved.  It  is  then  distilled  by  steam  with  the  addi- 
tion of  lime  to  break  up  ammonium  compounds,  and  led 
into  sulphuric  acid.  The  solution  of  ammonium  sulphate  is 
evaporated  and  the  white  or  gray  salt  which  results  is  dried 
and  sold  as  sulphate  of  ammonium,  largely  for  fertilizing 
purposes. 

(6)  Availability. — ^Ammonium  sulphate  is  almost  as  solu- 
ble as  sodium  nitrate,  one  part  dissolving  in  about  one  and 
one-third  parts  of  water,  but  for  most  plants  it  is  not  the  best 
form  of  nitrogen.  The  ammonia  nitrogen  must  first  change 
to  nitrate  nitrogen  which  it  does  very  rapidly  in  the  soil 
by  the  process  called  nitrification  (Section  123).  Its  ready 
solubility  and  rapid  change  to  nitrate  make  it  only  slightly 
less  readily  available  than  sodium  nitrate,  and  it  is  ranked 
as  a  quick-acting  fertilizer.  In  the  early  spring,  however,  to 
start  wheat,  for  example,  ammonium  sulphate  is  not  good 
because  at  that  time  of  year  bacterial  action  is  very  slow 
and  nitrification  does  not  take  place  with  sufficient  rapidity 
to  feed  the  crop.    A  nitrate  is  better  under  these  conditions. 

Ammonia  nitrogen  is  not  leached  from  the  soil  as  rapidly 
as  nitrate  nitrogen,  being  absorbed  both  chemically  and 
physically  (Section  131).  Ammonia,  held  either  in  other 
chemical  combinations  or  absorbed  by  humus  or  hydrated 
silicates,  is  just  as  easily  nitrified  as  it  is  in  the  sulphate 
form.  Until  nitrified,  ammonium  sulphate  is  not  lost  from 
the  soil,  but  nitrification  is  ordinarily  so  rapid  that  ammo- 
nium sulphate  is  not  a  lasting  nitrogenous  fertilizer. 

(c)  Effect  on  the  Soil. — Whereas  sodium  and  calcium 
nitrates  tend  to  produce  a  residual  alkaline  condition  of 
the  soil,  ammonium  sulphate  tends  to  produce  an  acid  con- 
dition. Long  continued  use  of  this  form  of  nitrogen  results 
in  a  very  acid  condition  of  the  soil.  On  the  fertilizer  plats 
of  the  Pennsylvania  Experiment  Station  the  use  of  72  pounds 
of  nitrogen  as  ammonium  sulphate  per  acre  once  in  two  years 
for  thirty  years  has  resulted  in  a  soil  which  needs  19  times 
as  much  lime  to  correct  the  acidity  as  do  the  check  plats 
receiving  no  fertilizer. 

In  nitrifying,  the  ammonia  is  changed  to  nitric  acid,  and 
sulphuric  acid  is  set  free.     Both  acids  require  bases  to 


200 


NITROGENOUS  FERTILIZERS 


neutralize  them,  and  thus  there  is  twice  as  much  hme  or  other 
base  needed  for  this  fertihzer  as  is  needed  for  other  nitrog- 
enous materials  undergoing  nitrification.  Lime  is  used  up 
very  rapidly  and  acidity  results  (Section  177). 

m.    NITROGEN  AS  AMINE  OR  PROTEIN 

152.  Cyanamid  or  Lime  Nitrogen. — ^The  utilization  of 
atmospheric  nitrogen  in  the  manufacture  of  fertilizers  is 
successfully  accomplished  in  another  way  than  those  men- 
tioned in  Section  150.  The  process  depends  on  the  fact  that 
nitrogen  unites  with  calcium  carbide  to  form  calcium  cyana- 
mide  at  a  temperature  about  1000°  C.  in  the  soil  this  com- 
pound changes  gradually  to  nitrate.  This  fertilizer  goes 
under  a  variety  of  names.    Cyanamid  is  the  trade  name  of  the 


Fig.  51. — Plant  of  American  Cyanamid  Co.,  Niagara  Falls 


American  product  manufactured  at  Niagara  Falls  (Fig.  51). 
Calcium  cyanamide  is  a  common  name  for  it,  although  as  a 
matter  of  fact  the  fertilizer  contains  only  about  45  per 
cent,  of  this  compound.  Lime  nitrogen  is  another  name; 
also  nitrolim  which  is  the  trade  name  of  the  fertilizer  sold 
in  England. 


NITROGEN  AS  AMINE  OR  PROTEIN  201 

(a)  How  Made, — Calcium  carbide  is  first  made  by  fusing 
in  an  electric  furnace  a  mixture  of  coke  and  lime.  The 
reaction  is  as  follows : 

CaO  +  3C  =  CaC2  +  CO. 

The  carbide  is  removed,  cooled,  crushed  to  a  fine  powder 
and  placed  in  perforated  steel  cans  set  in  brick  oveng.  A 
carbon  rod  carrying  a  current  of  electricity,  and  passing 
through  the  center  of  the  can  serves  to  heat  up  the  carbide 
to  about  1100°  C,  when  union  takes  place  between  the 
carbide  and  a  stream  of  pure  nitrogen  which  is  gently  forced 
into  the  can.    The  reaction  is  as  follows: 

CaC2  +  N2  =  CaCNa   +  C. 

Pure  nitrogen  is  obtained  by  passing  air  over  red  hot 
copper  when  the  oxygen  unites  with  the  copper  to  form 
copper  oxide  and  the  nitrogen  alone  issues  from  the  furnace. 
The  best  process,  however,  is  to  fractionally  distill  liquid 
air.  Nitrogen  boils  at  — 195.5°  C.  and  oxygen  at  — 182.5°  C. 
The  nitrogen  comes  off  first  and  can  be  obtained  very  pure. 

The  nitrogenous  product,  which  is  really  an  impure  calcium 
cjanamide,  is  next  cooled,  pulverized,  and  treated  with 
water  in  rotating  cylinders.  About  30  per  cent,  of  water 
is  taken  up,  the  excess  of  calcium  oxide  is  hydrated,  and  a 
little  carbide  decomposed  to  acetylene  and  hydrated  calcium 
oxide.  The  material  is  then  pressed  into  bricks  and  before 
use  is  crushed  and  screened  so  that  a  granulated  fertilizer 
is  obtained  which  is  made  use  of  almost  exclusively  in 
manufacturing  complete  fertilizers.  The  cyanamid  as  it 
comes  on  the  market  contains  about  45  per  cent,  of  calcium 
cyanamide,  15  per  cent,  nitrogen,  27  per  cent,  calcium 
hydroxide,  and  13  per  cent,  free  carbon,  besides  small 
amounts  of  other  constituents. 

(b)  Availability. — ^The  fertilizing  compound  in  cyanamid 
is  calcium  cyanamide:  Ca  =  N— C  =  N.  This  compound  is 
soluble  in  water  but  not  available  to  plants.  Before  its  use 
by  plants  it  must  be  nitrified  and  this  process  takes  place 
in  five  stages  as  follows: 


202  NITROGENOUS  FERTILIZERS 

First,  hydrolysis  to  cyanamide  and  calcium  hydroxide, 
helped  probably  by  the  adsorptive  processes  in  the  soil,  thus : 

CaCN2+  2H2O  =  H2CN2  +  Ca(0H)2. 

The  calcium  hydroxide  is  changed  rapidly  to  carbonate. 

Second,  the  hydrolysis  of  cyanamide  with  the  aid  of 
collc^dal  catalysts  to  urea,  thus: 

H2CN2+ H2O  =  CO(NH2)2. 

Third,  the  bacterial  hydrolysis,  or  ordinary  ammonifying 
process,  to  ammonium  carbonate,  thus: 

CO(NH2)2+ 2H20  =  (NH4)2C03. 

Fourth,  nitrification  to  nitrous  acid  and  nitrites. 

Fifth,  further  nitrification  to  nitric  acid  and  nitrates. 

Cyanamid  is  ranked  as  a  fairly  quick  acting  fertilizer, 
about  as  good  as  ammonium  sulphate. 

(c)  Effect  on  the  Soil. — Cyanamid  while  producing 
nitric  acid  also  carries  considerably  more  calcium  oxide  than 
is  necessary  to  neutralize  this  acid.  The  residual  effect  is 
like  that  of  basic  calcium  nitrate,  and  is  beneficial.  Cases 
have  been  reported  where  cyanamid  has  harmed  crops,  but 
under  ordinary  farming  conditions  no  danger  from  it  need 
be  feared. 

153.  Dried  Blood. — By  evaporating,  drying,  and  grinding 
animal  blood  from  slaughter  houses  there  is  obtained  a 
product  known  as  dried  blood  which  is  one  of  the  best 
organic  nitrogenous  fertilizers.  It  comes  on  the  market  in 
two  forms,  red  and  black,  the  color  depending  on  the  processes 
of  manufacture.  Red  dried  blood  is  the  better  of  the  two, 
being  more  uniform  in  composition,  containing  more  nitrogen 
and  being  more  available  as  a  fertilizer.  Its  nitrogen  content 
is  approximately  13  per  cent.  Black  dried  blood  is  not  so 
pure,  being  often  mixed  with  hair,  dirt,  and  other  substances 
which  impair  its  value.  Its  nitrogen  content  varies  greatly, 
running  from  6  to  12  per  cent.  It  may  also  carry  3  or  4 
per  cent,  of  phosphoric  acid. 


NITROGEN  AS  AMINE  OR  PROTEIN  203 

The  availability  of  the  best  grades  of  dried  blood  is  roughly 
three-fourths  that  of  sodium  nitrate,  although  it  varies  with 
soil  conditions.  Its  nitrogen  is  in  the  protein  form  and  must 
undergo  the  complete  process  of  ammonification  and  nitri- 
fication before  becoming  available.  In  cold,  acid  soils  this 
process  is  not  so  rapid  and  as  a  result  dried  blood  is  not  a 
good  fertilizer  for  such  soils.  The  nitrogen  is  not  lost  from 
soils  since  leaching  cannot  take  place  except  as  the  protein 
nitrifies,  and  this  is  not  rapid  enough  to  cause  loss. 

Dried  blood  has  no  marked  effect  on  the  soil,  except  that 
its  tendency  is  toward  making  a  soil  acid,  it  being  organic 
in  nature  and  the  decomposition  of  organic  matter  produces 
organic  acids.  Nitrification  also  produces  acids  which  must 
be  neutralized.  But  it  must  be  remembered  that  the  natural 
tendency  of  cultivated  and  fertilized  soils  is  toward  acidity 
and  this  condition  should  not  be  feared.  Plenty  of  calcium 
carbonate  in  the  soil  prevents  acidity  from  appearing  and 
liming  will  overcome  this  condition  if  necessary  (See  Chapter 
XII). 

154.  Dried  Meat,  Meat  Meal. — lief  use  meat  from  slaughter 
houses  and  packing  houses,  and  waste  from  beef  extract 
factories  are  first  rendered,  that  is,  steamed  under  pressure 
to  remove  fat,  then  dried  and  ground.  Sometimes  bones  are 
mixed  with  the  meat  before  rendering,  and  in  this  case, 
of  course,  the  product  contains  phosphoric  acid.  The  best 
grades  of  dried  meat  carry  13  or  14  per  cent,  of  nitrogen, 
although  many  samples  run  less. 

The  availability  of  meat  meal  is  not  quite  so  high  as  dried 
blood,  but  it  makes  a  very  satisfactory  nitrogenous  fertilizer 
when  rapid  availability  is  not  wanted.  Its  nitrogen  is  in  the 
protein  form  and  like  that  of  dried  blood  is  not  lost  by 
leaching.  Its  effect  on  the  soil  is  similar  to  that  of  dried 
blood. 

155.  Tankage. — Besides  the  refuse  meat  there  are  other 
waste  animal  products  that  are  used  as  fertilizers.  Tendons, 
intestines,  lungs,  and  hair,  together  with  bones,  horns,  and 
hoofs  are  treated  with  steam  under  pressure  to  remove  fat 
and  gelatine,  then  dried  and  ground.  If  little  or  no  bone  is 
present  the  product  is  called  meat  tankage.    If  considerable 


204  NITROGENOUS  FERTILIZERS 

bone  is  present  it  is  called  bone  tankage.  Tankage  is  very 
variable  in  composition,  sometimes  containing  as  much  as 
12  per  cent,  nitrogen  in  meat  tankage,  and  up  to  9  per 
cent,  nitrogen  with  17  per  cent,  phosphoric  acid  in  bone 
tankage. 

Tankage  is  an  excellent,  rather  slow  acting  fertilizer,  its 
value  depending,  especially  in  the  case  of  bone  tankage,  on 
fineness  of  grinding.  The  nitrogen  is  in  the  same  form  as  in 
dried  meat  and  the  effect  on  the  soil  is  the  same. 

156.  Dried  Fish,  Fish  Scrap. — ^The  refuse  material  from 
fish  oil  refineries,  fish  salting,  or  canning  plants  is  dried 
and  ground,  sometimes  being  treated  with  dilute  sulphuric 
acid  to  stop  decomposition  and  partially  dissolve  the  bones. 
This  fertilizer  contains  from  6  to  9  per  cent,  nitrogen  and 
5  to  9  per  cent,  phosphoric  acid.  Fish  scrap  is  about  as  good 
as  the  better  grades  of  tankage,  though  slower  acting  than 
dried  blood.    It  contains  the  protein  form  of  nitrogen. 

157.  C!ottonseed  Meal. — The  press  cake  which  results  from 
the  extraction  of  oil  from  cotton  seed  is  used  extensively 
as  a  fertilizer.  The  decorticated  meal  made  from  seeds 
which  have  had  the  husks  removed  before  pressing,  runs 
about  6  per  cent,  nitrogen;  the  undecorticated  meal  carries 
only  4  per  cent,  nitrogen.  There  are  also  small  amounts 
of  phosphoric  acid  and  potash.  Since  cottonseed  meal  is  an 
excellent  cattle  food,  and  since  most  of  its  fertilizing  con- 
stituents are  recovered  in  the  manure,  it  is  much  more 
profitable  to  feed  it  first  and  use  the  manure  as  a  fertilizer. 
But  it  is,  nevertheless,  used  to  a  very  large  extent  directly 
as  a  fertilizer,  especially  in  the  south.  Moreover,  its  physical 
condition  is  such  that  it  improves  the  mechanical  condition 
of  mixed  fertilizers  by  absorbing  moisture  and  preventing 
caking.  Its  availability  is  about  the  same  as  dried  blood 
and  the  form  of  nitrogen  is  similar. 

158.  Castor-Bean  Pomace. — ^This  is  the  ground  press  cake 
from  the  manufacture  of  castor  oil,  and  contains  about 
5  per  cent,  nitrogen  with  some  phosphoric  acid  and  potash. 
It  is  a  good  fertilizer. 

159.  Leather,  Hair,  Wool  Waste,  Hoof,  and  Horn. — ^These 
materials  are  waste  products  from  various  industries  and 
are  very  slow  acting,  practically  worthless  forms  of  nitrog- 


EXERCISES  205 

enous  fertilizers  when  used  without  previous  treatment. 
Leather,  hoof,  and  horn  are  sometimes  steamed  or  roasted 
and  ground,  and  even  treated  with  sulphuric  acid,  when  they 
make  a  fair  grade  of  fertilizer.  Leather  contains  about  8 
per  cent,  nitrogen,  hair  13  per  cent.,  wool  waste  5  to  10 
per  cent.,  horn  and  hoof  10  to  15  per  cent. 

Most  of  these  materials,  however,  are  used  by  the  fertilizer 
manufacturers  in  the  preparation  of  "base  goods."  They  are 
treated  with  sulphuric  acid  along  with  rock  phosphate. 
The  nitrogen  is  thereby  partly  converted  to  ammonium  sul- 
phate or  some  more  available  form  of  nitrogen  than  the 
original  non-decomposible  protein  form.  This  mixture  of 
acid  phosphate  and  "chamber  process"  nitrogenous  material 
forms  a  "  base"  for  fertilizer  mixtures. 

EXERCISES 

1.  What  is  the  relative  availability  of  the  following  fertilizers:  sodium 
nitrate,  ammonium  sulphate,  dried  blood,  hair?  Prove  your  statement 
by  showing  that  each  in  succession  must  undergo  more  changes  than  the 
preceding  one  before  it  becomes  available  to  plants.  Which  of  these  has  a 
tendency  to  leave  the  soil  acid  and  why? 

2.  Describe  briefly  three  widely  different  ways  of  changing  the  atmos- 
pheric nitrogen  into  available  plant  food. 

3.  Why  should  nitrate  and  not  dried  blood  be  used  in  early  spring? 
Which  makes  the  better  top  dressing  and  why? 

4.  Suppose  a  soil  is  lacking  in  available  nitrogen  and  nitrogenous  fertil- 
izers are  not  to  be  had,  state  in  detail  how  a  crop  of  cabbage  might  suffer. 

5.  Is  it  wise  to  apply  enough  sodium  nitrate  to  last  for  the  four  crops  once 
in  a  rotation  of  corn,  oats,  wheat  and  grass?     Why  or  why  not? 

6.  To  what  extent  has  man  imitated  Nature  in  the  making  of  nitrogenous 
fertilizers? 

7.  Which  contains  the  most  nitrogen  per  ton,  sodium  nitrate,  96  per  cent, 
pure,  pure  ammonium  sulphate,  or  pure  ammonium  nitrate? 

8.  In  how  many  respects  is  the  process  of  making  cyanamid  available 
similar  to  that  of  making  a  protein  available? 

9.  Is  cyanamid  an  organic  compound?  If  so,  what  kind  of  an  organic 
compound?     Is  cyanamid  a  name  descriptive  of  its  composition? 

10.  Dried  blood  and  hair  both  contain  nitrogen  in  the  protein  form. 
Why  is  there  such  a  difference  in  their  availability? 

11.  Refuse  meats  are  first  rendered  in  the  making  of  meat  meal.  Why 
does  this  process  make  a  better  fertilizer? 

12.  Can  you  suggest  why  the  following  are  not  mentioned  as  nitrogenous 
fertilizers:    Ammonium  chloride,  ammonium  carbonate,  potassium  nitrate? 

13.  What  crops  remove  the  most  nitrogen  per  acre? 

REFERENCES 
See  references  at  end  of  Chapter  VIII. 


CHAPTER  X 
PHOSPHATE  FERTILIZERS 

Of  all  the  fertilizing  elements  which  the  farmer  buys 
phosphorus  is  the  one  which  should  and  does  cause  him  the 
greatest  concern.  The  soil  contains  no  more  phosphoric  acid 
than  nitrogen,  the  average  of  good  cultivated  soil  being  not 
far  from  0.15  to  0.2  per  cent.  Phosphorus  is  necessary 
for  the  production  of  seed,  inducing  early  and  full  maturity. 
It  occurs  for  the  most  part  in  the  grain  at  harvest  and  is 
thereby  sold  from  the  farm,  little  being  left  in  stems  and 
leaves  to  be  returned  to  the  soil  as  litter.  Finally,  phos- 
phorus cannot  be  added  to  the  soil  by  the  growth  of  any 
special  crop.  It  is  not  like  nitrogen  which  can  be  obtained 
by  legumes  from  the  exhaustless  atmospheric  source.  Phos- 
phorus must  be  purchased  and  added  to  the  soil,  or  the  soil 
becomes  exhausted.  Supplies  brought  up  from  the  subsoil 
either  by  capillarity  or  the  growth  of  deep-rooted  crops 
are  not  sufficient  to  add  materially  to  the  amount  in  the 
surface  soil.  Continued  cropping  and  no  return  result  in 
a  loss  of  phosphorus.  Phosphate  fertilizers,  then,  are  of 
prime  importance. 

160.  Raw  Bone. — Bones  when  fresh  contain  about  40 
per  cent,  of  organic  matter,  53  per  cent,  of  inorganic  matter 
and  7  per  cent,  of  water.  The  organic  matter  consists  of 
fat  and  ossein,  the  latter  a  protein.  The  inorganic  matter 
is  mostly  tricalcium  phosphate,  Ca3(P04)2.  It  comes  on 
the  market  as  raw  bone-meal,  and  coarse  ground  bone,  con- 
taining about  4  per  cent,  nitrogen  and  22  per  cent,  phos- 
phoric acid.  The  presence  of  the  fat  makes  fine  grinding 
impossible  and  it  is  not  used  much  as  a  fertilizer.  The 
fat  prevents  bacterial  action,  thus  checking  nitrification,  and 
together  with  the  ossein  protecting  the  phosphate  from  being 
acted  upon  by  soil  solvents. 
(206) 


DISSOLVED  BONE-BLACK  207 

161.  Steamed  Bone,  Bone-Meal. — The  fat  in  bone  is 
valuable  for  various  commercial  purposes  and  the  ossein 
can  be  converted  into  gelatine  and  glue.  There  are  two 
ways  of  removing  fat:  By  extraction  with  a  solvent  like 
benzine;  or  by  treatment  with  boiling  water  or  steam  under 
pressure.  Subsequent  cooling  allows  the  fat  to  solidify  on  top 
of  the  water,  and  to  be  removed.  Steaming  under  pressure 
also  converts  ossein  to  gelatine,  soluble  in  water.  The  bone 
that  is  left  can  be  dried  and  easily  ground  fine.  This  material 
is  sold  as  steamed  bone-meal  or  bone-meal.  The  best 
grades  contain  25  to  30  per  cent,  of  phosphoric  acid,  but 
frequently  less  than  1  per  cent,  nitrogen.  The  removal  of 
fat  and  ossein  leaves  the  tricalcium  phosphate  in  much 
better  physical  condition  both  for  grinding  and  subsequent 
solution  in  the  soil.  Steamed  bone-meal  is  a  very  excellent 
phosphate  fertilizer  and  fairly  available. 

Bone  products  have  had  a  value  as  a  fertilizer  for  centuries 
and  even  now  are  considered  by  many  to  be  superior  to  other 
forms  of  phosphate,  consequently  the  temptation  to  adulter- 
ate bone-meal  with  worthless  substances  has  been  very 
great.  This  fact  together  with  differences  in  method  of 
treatment  and  quality  of  original  bones  makes  the  product 
one  of  great  variation  in  phosphoric  acid  content.  The 
figures  given  are  average  for  a  good  product. 

162.  Bone-Black. — When  bones  are  subjected  to  destruc- 
tive distillation,  the  organic  matter  is  largely  driven  oft'  and 
there  remains  the  inorganic  matter  and  about  10  per  cent, 
of  carbon.  This  material  is  known  as  bone-black,  or  animal 
charcoal,  and  on  account  of  its  porosity  and  adsorptive  power 
is  used  after  grinding  for  clarifying  sugar  solutions  in  sugar 
refineries,  and  for  other  similar  purposes.  But  little  of  it  is 
used  as  fertilizer  in  the  freshly  made  form,  most  of  it  being 
first  employed  as  above  stated. 

After  a  time  it  loses  its  adsorptive  or  clarifying  power  and 
then  is  sold  as  a  fertilizer,  although  the  presence  of  the 
carbon  prevents  ready  solution  of  the  tricalcium  phosphate. 
It  contains  about  30  per  cent,  phosphoric  acid. 

163.  Dissolved  Bone-Black. — If  the  spent  bone-black 
above  mentioned  is  treated  with  sulphuric  acid,  it  becomes  a 


208  PHOSPHATE  FERTILIZERS 

readily  available  phosphate  fertilizer,  being  converted  into 
monocaleium  phosphate  which  is  soluble  in  water,  whereas 
tricalcium  phosphate  is  only  slowly  soluble  in  water  and 
carbon  dioxide.    The  reaction  may  be  expressed  thus: 

Cas(P04)2+  2H2SO4  =CaH4(P04)2+2CaS04 

'  Its  content  of  phosphoric  acid  is  about  14  to  16  per  cent. 

164.  Rock  Phosphate,  Floats. — Originally  the  name  "floats" 
was  applied  to  a  particularly  fine  ground  rock  phos- 
phate, so  fine  that  it  would  float  in  the  air.  Now,  however, 
the  term  is  loosely  used  for  any  finely  ground  rock  phosphate. 
Deposits  of  phosphate  rock  are  found  in  many  places.  In 
France,  Belgium,  Portugal,  and  North  Africa  there  are 
beds  of  greater  or  less  thickness.  The  greatest  supply, 
however,  comes  from  Florida,  South  Carolina  and  Ten- 
nessee. Recently  there  have  been  discovered  immense  beds 
in  Idaho,  Wyoming,  and  Montana.  These  constitute  a 
reserve  supply  of  great  importance  since  the  older  mines 
are  being  rapidly  exhausted.  In  South  Carolina  and 
Florida  the  phosphate  occurs  largely  as  pebbles  or  boulders 
in  deposits  resembling  gravel  beds  (Fig.  52).  In  Tennessee 
it  occurs  in  veins  or  pockets. 

The  phosphorus  occurs  as  tricalcium  phosphate  together 
with  varying  amounts  of  iron  and  aluminium  compounds 
and  calcium  carbonate.  The  phosphoric  acid  content 
varies  from  25  to  40  per  cent.,  iron  and  aluminium  oxide, 
2  to  6  per  cent.,  and  calcium  carbonate  from  1  or  2  per  cent, 
to  10  or  15  per  cent. 

As  a  fertilizer,  rock  phosphate  is  very  slow  acting  when 
applied  alone.  The  finer  it  is,  the  more  valuable  it  becomes, 
but  even  very  finely  ground  it  is  best  used  in  connection 
with  decaying  organic  matter.  Applied  to  acid  peat  or  muck 
soils  it  is  especially  good,  and  when  mixed  with  manure 
gives  excellent  results.  Opinion  is  divided  as  to  its  value 
compared  to  acid  phosphate,  even  when  mixed  with  manure. 
Whether  or  not  it  is  as  good  as,  or  better  than,  acid  phosphate 
when  similarly  mixed  with  manure,  it  is,  nevertheless,  a  most 
excellent  phosphatic  manure.  Its  cheapness  recommends 
it,  as  well  as  its  high  content  of  phosphoric  acid. 


ROCK  PHOSPHATE,  FLOATS 


209 


14 


210  PHOSPHATE  FERTILIZERS 

The  fermenting  mixture  of  rock  phosphate  and  manure 
has  never  showed  any  very  greatly  increased  solubiHty  of 
phosphoric  acid  under  laboratory  conditions  of  extraction, 
but  field  trials  have  abundantly  proved  that  this  mixture 
is  much  better  than  rock  phosphate  alone  or  than  manure 
alone,  showing  that  at  least  under  field  conditions  the  phos- 
phoric acid  is  rendered  sufficiently  soluble  for  the  growing 
plant. 

165.  Acid  Phosphate,  Superphosphate.— This  is  the  best 
known  form  of  phosphate  fertilizer. 

(a)  How  Made. — ^To  make  rock  phosphate  available  it 
is  treated  with  sulphuric  acid  which  converts  the  tricalcium 
phosphate  to  monocalcium  phosphate  according  to  the 
equation  given  under  Dissolved  Bone-Black.  The  finely 
ground  rock  phosphate  together  with  the  right  amount  of 
approximately  65  per  cent,  sulphuric  acid  is  placed  in 
mixing  chambers  provided  with  stirrers.  After  being 
thoroughly  mixed  the  material  is  dumped  into  "dens" 
where  the  reaction  is  completed.  Considerable  heat  is 
developed,  and  the  final  product  solidifies,  because  of  the 
formation  of  gypsum,  CaS04.2H20.  This  mass  after 
standing  for  some  time  is  crushed  fine  and  is  ready  for 
use. 

In  calculating  the  amount  of  acid  to  use,  due  regard  is 
paid  to  the  ingredients  other  than  tricalcium  phosphate. 
Calcium  carbonate,  of  course,  uses  up  sulphuric  acid  and  so 
do  the  iron  and  aluminium  compounds.  Iron  compounds, 
however,  interfere  with  the  formation  of  a  good  product, 
if  they  are  present  in  any  considerable  quantity — over  4  or 
5  per  cent.  The  resulting  mixture  is  in  bad  physical  con- 
dition on  account  of  the  formation  of  ferric  sulphate  and  of 
something  like  a  hydrated,  acid  iron  phosphate.  It  does 
not  dry  sufficiently  to  pulverize  easily.  Moreover,  insoluble 
iron  and  aluminium  phosphates  are  formed,  which,  of  course, 
are  worthless  as  quick  acting  fertilizers. 

Acid  phosphate  runs  from  12  to  16  per  cent,  phosphoric 
acid  with  14  per  cent,  as  the  average  content  of  available 
phosphoric  acid.     In  order  to  prevent  any  possible  excess 


ACID  PHOSPHATE,  SUPERPHOSPHATE  211 

of  sulphuric  acid  it  is  customary  to  add  somewhat  less  than 
the  theoretical  amount.  This  results  in  the  incomplete 
conversion  of  all  the  tricalcium  phosphate  to  monodalcium 
phosphate.  On  standing,  these  two  compounds  unite  to 
form  "reverted"  or  "gone  back"  phosphates.  That  is, 
the  water  soluble  monocalcium  phosphate  starts  to  revert 
or  go  back  to  the  tricalcium  phosphate  and  forms  dicalcium 
phosphate.  Since  the  latter  is  soluble  in  ammonium  citrate 
solution  (Section  201),  it  is  sometimes  called  citrate  soluble 
phosphoric  acid.    The  equation  is  as  follows: 

CaH4(P04)2+  Ca,(PO02=  2Ca2H2(P04)2. 

Reverted  phosphate  is  almost  as  available  as  the  mono- 
calcium  phosphate. 

(h)  Availability. — Acid  phosphate  is  a  quick  acting  fertil- 
izer, readily  available,  and  all  things  considered  is  the  best 
form  of  phosphate  to  use  under  ordinary  conditions. 

(c)  Effect  on  the  Soil. — In  the  soil  acid  phosphate 
reverts  very  quickly  to  dicalcium  and  tricalcium  phosphate. 
Notwithstanding  this  reversion,  which  takes  place  before 
the  plant  obtains  much  of  the  fertilizer,  acid  phosphate  is 
more  readily  available  than  tricalcium  phosphate  or  rock 
phosphate  for  two  reasons :  In  the  first  place,  acid  phosphate 
dissolves  in  the  soil  water  and  permeates  the  soil,  so  that 
when  it  is  precipitated  it  is  thoroughly  distributed.  This 
precipitate  is  much  finer  than  any  mechanically  ground 
material  and,  moreover,  is  much  better  mixed  with  the  soil. 
In  the  second  place,  freshly  precipitated  di-  or  tricalcium 
phosphate  is  much  more  soluble  in  water  and  carbon  dioxide 
than  is  tricalcium  phosphate  which  has  been  formed  for  a 
long  time,  like  the  rock  phosphate. 

Acid  phosphate  is  said  to  make  a  soil  acid.  This  surely 
is  not  due  to  the  fact  that  it  is  an  acid  salt,  for  the  plant  in 
the  long  run  uses  fully  as  much  phosphoric  acid  as  calcium, 
and  usually  more,  so  that  the  residual  effect  could  not  be 
acid.  Moreover,  although  it  may  use  up  bases  by  reversion 
in  the  soil,  these  bases  are  liberated  again  when  the  phosphate 


212  PHOSPHATE  FERTILIZERS 

redissolves  in  water  and  carbon  dioxide.  Some  authorities 
claim  that  the  acidity  is  due  to  the  presence  of  calcium 
sulphate,  a  necessary  by-product  in  the  manufacturing 
process.  But  it  is  doubtful  if  this  has  any  more  residual 
acid  effect  than  any  ordinary  fertilizer  or  than  any  normal 
soil  treatment. 

166.  Basic  Slag,  Thomas  Slag. — Basic  slag  is  a  very 
popular  fertilizer  in  Germany. 

(a)  How  Made. — In  the  basic  Bessemer  process  of  making 
steel  from  phosphatic  iron,  devised  by  Thomas  and  Gil- 
christ, of  England,  the  molten  cast  iron  is  placed  in  a  con- 
verter lined  with  calcium  oxide  or  calcium  and  magnesium 
oxides.  By  blowing  a  stream  of  air  through  the  molten 
mass,  phosphorus  and  silicon  are  oxidized  and  unite  with 
the  calcium  to  form  a  double,  basic  phosphate  and  silicate  of 
calcium.  The  molten  slag  is  poured  off  and  when  cool  is 
broken  up  and  jBnely  ground. 

(6)  Composition. — ^The  exact  compound  of  the  phos- 
phorus in  basic  slag  is  not  known,  but  there  have  been 
found  crystals  of  so-called  tetracalcium  phosphate.  Most 
of  the  phosphorus,  however,  is  probably  in  the  form  of  a 
pentacalcium  silico-phosphate.  These  compounds  may  best 
be  compared  with  the  other  compounds  of  calcium  and 
phosphorus  so  far  studied: 

l..Monocalcium  phosphate,  CaO.(H20)2.P206,  found  in 
dissolved  phosphates  such  as  acid  phosphate  and  dissolved 
bone-black. 

2.  Bicaldum  phosphate,  (CaO)2.H20.P205,  found  to  some 
extent  with  acid  phosphate  as  the  so-called  reverted  phos- 
phate. 

3.  Tricaldum  phosphate,  (CaO)3.P205,  found  in  rock 
phosphate  and  bones. 

4.  Tetracalcium  phosphate,  (CaO)4.P205,  and  penta- 
calcium silico-phosphate,  (CaO)5.Si02.P20B. 

The  formulas  for  the  first  three  have  here  been  modified 
from  their  usual  form  to  bring  out  the  differences  between 
them  and  the  last  two. 


BASIC  SLAG  213 

Now  to  illustrate  their  combination  graphically: 

H— o 

\ 
H— O— P-0 

/ 

o 

Monocalcium  phosphate  Ca^ 

O 

\ 
H— O— P=0 

/ 
H— O 

H— O 

\ 
H— O— P=0 
/ 
O 


Dicalcium  phosphate  Ca<' 

( 


o 

\ 

O— P=0 
Ca<' 


Ca<    \ 

^o— p=o 

/ 

Tricalcium  phosphate  Ca<' 

\o 

\ 
/O— P=0 
Ca< 


/ 

o 


o        o 

/  \  /  \ 

Ca  P  Ca 

\    /    \    / 

o        o 

Tetracalcium  phosphate  O 

O  O 

/    \l/    \ 
Ca  P  Ca 

\    /    \    / 
O  O 


214 


PHOSPHATE  FERTILIZERS 


O  O 

/  \   /  \ 
Ca  P  Ca 

O     I      O 

I 

Pentacalcium  silico-phosphate  O 

O 

/    ^ 
Ca  Si 

o 


o 


o 


/ 


o 


Ca  P  Ca 

\    /   \    / 

o        o 

(c)  Availability. — Basic  slag  is  usually  considered  about 
one-half  as  available  as  acid  phosphate,  although  on  acid 
soils  it  is  much  more  readily  soluble  and  quick  acting.  It  is 
considered  an  excellent  form  of  phosphate.  In  this  country 
its  use  is  limited  by  few  importations  and  relatively  high 
price.  Iron  ores  in  this  country  are  too  low  in  phosphorus 
to  produce  a  slag  from  steel  that  is  valuable  as  a  fertilizer. 
In  Europe,  on  the  other  hand,  the  slags  are  rich  in  phos- 
phorus, the  phosphoric  acid  content  running  from  10  to 
20  per  cent. 

(d)  Effect  on  the  Soil. — Basic  slag  was  formerly  thought 
to  have  considerable  free  lime,  since  it  was  basic  in  character 
and  was  excellent  on  an  acid  soil.  As  a  matter  of  fact  it 
contains  only  a  few  per  cent,  of  free  calcium  oxide  (1  to  6 
per  cent.).  The  decomposition  of  the  basic  slag  in  the  soil, 
however,  results  in  the  production  of  calcium  carbonate. 
The  action  of  water  and  carbon  dioxide  produces  di-  or  tri- 
calcium  phosphates  and  bicarbonate  of  calcium,  in  addition 
to  silicic  acid  or  free  silica.  In  this  way  basic  slag  acts  as  a 
neutralizer  of  soil  acidity,  and  an  improver  of  soil  texture. 
There  is  not,  however,  enough  calcium  carbonate  resulting 
from  an  ordinary  application  of  basic  slag — say  500  or  600 
pounds — to  entirely  correct  the  acidity  of  an  ordinarily 


REFERENCES  215 

sour  soil.  In  such  an  application  there  probably  would  not 
result  more  than  100  pounds  of  calcium  oxide  combined  as 
carbonate,  not  enough  for  any  immediate  effectiveness. 

EXERCISES 

1.  Why  is  there  a  difference  in  the  availability  of  rock  phosphate,  raw 
bones  and  steamed  bone  meal? 

2.  Compare  mono-,  di-,  and  tri-calcium  phosphate  as  to  formula,  solu- 
bility and  availability.  How  does  industry  change  one  into  the  other? 
How  does  the  soil  accomplish  the  same  thing?  Can  the  soil  accomplish 
the  opposite  effect?     Which  is  the  better  for  the  farmer  to  use  and  why? 

3.  In  making  acid  phosphate  from  rock  phosphate  what  components 
are  taken  into  account  and  why? 

4.  Suppose  a  soil  was  in  such  a  state  that  available  PjOt  was  lacking, 
and  fertilizer  was  not  to  be  had,  state  in  detail  how  a  crop  of  wheat  might 
suffer. 

5.  What  is  the  value  of  mixing  organic  matter  with  rock  phosphate? 

6.  Explain  why  an  acid  soil  usually  lacks  available  phosphorus. 

7.  Is  much  basic  slag  produced  in  this  country?     Why? 

8.  Is  reversion  of  acid  phosphate  a  phenomenon  that  is  desirable?  very 
harmful?  that  can  be  prevented  in  an  alkaline  soil?  that  can  happen  in  an 
acid  soil?  that  prevents  leaching?  that  is  an  example  of  absorption?  that 
permits  the  addition  of  sufficient  acid  phosphate  to  a  soil  once  in  a  rotation? 

9.  What  crops  remove  the  most  phosphoric  acid  per  acre? 


REFERENCES 
See  references  at  end  of  Chapter  VIII. 


CHAPTER  XI 
POTASH  FERTILIZERS 

The  third  of  the  fertiHzer  trio  is  potassium  or,  as  it  is 
usually  called,  potash.  The  element  potassium  occurs  in 
most  soils  to  a  very  considerable  extent  (Section  138  b,  6), 
but  it  is  frequently  present  in  an  unavailable  form.  Some 
plants,  notably  clover  and  alfalfa,  require  considerable 
potassium;  and  other  crops  also  remove  it  to  no  small 
extent.  Unlike  nitrogen  and  phosphorus,  however,  potas- 
sium is  not  sold  from  the  farm  in  any  considerable  amount 
except  in  hay,  since  it  occurs  for  the  most  part  in  the  stems 
and  leaves  of  plants.  These  are  the  portions  of  the  crop 
which  usually  remain  on  the  farm,  being  fed  as  roughage  or 
used  as  litter.  In  this  way  the  potassium  gets  back  to  the 
soil.  Its  application,  however,  frequently  results  in  increased 
yields,  and  it  is  thus  an  important  element  in  fertilizers.  In 
the  past,  however,  there  has  been  a  tendency  to  use  too  much 
potash,  a  fault  corrected  by  the  Great  War  which  caused 
a  serious  lack  of  potash  fertilizers.  Farmers  have  learned 
that  general  farm  crops,  as  a  rule,  need  little  or  no  potash. 
Special  crops  like  potatoes  and  tobacco  and  intensive  crops 
need  some  potash. 

167.  The  German  Potash  Deposits. — ^The  most  important 
source  of  potassium  in  the  world  is  located  at  Stassfurt  in 
northern  Germany  where  there  are  today  over  one  hundred 
mines  producing  potash  salts  (Fig.  53) .  For  several  centuries 
common  salt  had  been  obtained  from  its  salt  springs  and 
wells.  About  the  middle  of  the  nineteenth  century  deep 
borings  revealed  the  presence  of  immense  beds  of  rock  salt 
at  a  depth  of  about  1000  feet.  Overlying  these  beds  of  salt, 
however,  were  considerable  deposits  of  potassium  and 
magnesium  compounds.  These  salts  were  considered  worth- 
less at  the  time  and  were  thrown  away,  but  later  their  value 
(216) 


THE  GERMAN  POTASH  DEPOSITS 


217 


became  apparent,  until  now  the  potash  salts  are  the  only 
ones  of  value.    Rock  salt  is  no  longer  mined  at  Stassfurt. 


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218  POTASH  FERTILIZERS 

It  is  believed  that  in  past  geologic  ages  there  existed 
here  an  immense  inland  sea  which  was  probably  fed  inter- 
mittently by  inrushes  of  water  from  the  ocean.  The 
climate  of  Europe  at  that  time  was  tropical  and  evapora- 
tion of  water  from  this  sea  was  consequently  rapid.  The 
water  became  more  and  more  concentrated  in  salts  until 
finally  the  least  soluble  were  deposited.  On  top  of  these 
compounds  other  salts  were  deposited  layer  by  layer. 
Intermittent  additions  of  sea  water  from  outside  caused  a 
dilution  of  the  water  within,  and  deposition  of  salt  was 
consequently  interrupted,  causing  alternate  layers  of  less 
soluble  and  more  soluble  compounds  as  evaporation  went 
on.  Geologic  changes  brought  about  the  deposition  of 
various  sedimentary  rocks  and  finally  a  layer  of  impervious 
clay  which  protected  the  soluble  salts  from  solution  in  rain 
water. 

The  bottom  layers  of  these  beds  are  composed  of  anhydrite 
(sulphate  of  calcium)  and  rock  salt.  Next  comes  the  so-called 
polyhalite  region  (sulphates  of  calcium,  magnesium,  and 
potassium) ;  then  the  kieserite  region  (magnesium  sulphate) ; 
and  finally  the  carnallite  region  (chlorides  of  potassium  and 
magnesium).  The  last  is  a  bed  ranging  from  50  to  130 
feet  in  thickness,  from  which  most  of  the  potash  salts  are 
obtained.  Due  to  the  intermittent  deposition  of  salts, 
partial  solution  from  infiltration  of  rainwater,  and  redepo- 
sition,  the  layers  of  salts  are  not  perfectly  distinct  and  not 
always  in  the  same  order.  For  instance,  layers  of  anhydrite 
and  rock  salt  intersperse  the  other  salts,  together  with 
minerals,  such  as  sylvine  (potassium  chloride)  and  kainite 
(sulphate  and  chloride  of  magnesium  and  potassium). 

168.  Muriate  of  Potash,  Potassium  Chloride,  KCl. — This  is 
the  most  widely  used  potash  fertilizer.  It  is  manufactured 
from  carnallite  which  occurs  mixed  with  rock  salt  and  other 
minerals,  and  contains  only  9  per  cent,  actual  potash. 
By  dissolving  carnallite  in  hot  magnesium  chloride  solution, 
boiling,  and  crystallizing,  there  is  obtained  a  muriate  con- 
taining about  20  per  cent,  potash  and  called  Potash  Manure 
Salt.  On  further  evaporation  and  crystallization  of  the 
mother  liquor  a  pure  carnallite  (KCl.MgCl2.6H2O)  is  obtained 


MURIATE  OF  POTASH,  POTASSIUM  CHLORIDE     219 

(Fig.  54).  This  salt  on  being  treated  just  like  the  crude 
carnallite  yields  the  commercial  muriate  with  one  crystalli- 
zation. 


220  POTASH  FERTILIZERS 

There  are  three  grades  of  muriate  on  the  market,  80  per 
cent.,  95  per  cent.,  and  98  per  cent.,  which  contain  respec- 
tively 50.5  per  cent.,  60  per  cent.,  and  61.9  per  cent,  potash 
(K2O).  The  80  per  cent,  muriate  is  the  one  usually  sold, 
however. 

It  is  very  generally  stated  that  potassium  chloride  affects 
the  burning  quality  of  tobacco  and  makes  potatoes  watery. 
The  former  is  probably  true,  but  the  latter  is  not  always  the 
case,  for  excellent  potatoes  can  be  grown  with  the  chloride, 
provided,  however,  that  lime  has  been  applied  to  the  soil. 
The  bad  effects  of  the  chlorine  are  apparently  most  pro- 
nounced on  acid  soils. 

The  tendency  of  potassium  chloride  is  to  make  a  soil 
acid  (Section  177).  Plants  exercising  their  selective  action 
remove  the  base,  potassium,  from  the  soil  and  leave  the 
chlorine  which  is  assimilated  but  little.  This  results  in  the 
production  of  hydrochloric  acid  which  neutralizes  any  basic 
compound  present  in  the  soil,  and  this  means  usually  calcium 
carbonate.  When  the  reserves  of  base  are  used  up  the  soil 
becomes  acid.  The  calcium  chloride  thus  formed  is  easily 
leached  from  the  soil.  Potassium  chloride  removes  calcium 
from  the  soil  in  another  way  by  reacting  with  calcium 
silicates  to  form  potassium  silicates  and  calcium  chloride 
which  is,  of  course,  leached  out. 

169.  Sulphate  of  Potash,  Potassium  Sulphate,  K2SO4. — This 
fertilizer,  although  not  used  to  so  great  an  extent  as  the 
muriate,  is  in  many  respects  the  best  one  to  employ.  It  is 
made  by  dissolving  and  concentrating  a  mixture  of  potassium 
chloride  and  kieserite  (magnesium  sulphate).  There  is 
precipitated  the  double  sulphate  of  potassium  and  magnesium 
(K2S04.MgS04),  which  is  also  sold  under  the  name  of  Double 
Potash  Manure  Salt,  containing  about  27  per  cent,  potash. 
This  double  salt  is  further  dissolved  with  a  certain  amount 
of  potassium  chloride  and  boiled.  Potassium  sulphate  is 
precipitated.  Two  grades  are  sold,  90  and  96  per  cent,  pure, 
containing,  respectively,  47 .  per  cent.,  and  52.7  per  cent, 
potash. 

Potassium  sulphate  has  no  bad  effects  on  tobacco  and 
potatoes,  and,  furthermore,  is  not  so  apt  to  make  a  soil  acid, 


NATURAL  BRINES  221 

since  plants  assimilate  sulphur  to  a  considerable  extent. 
The  whole  salt  is  thus  absorbed  and  no  residue  left.  This 
fertilizer  has  an  action  on  calcium  silicates  similar  to  that 
of  the  chloride,  but  the  resulting  calcium  sulphate  is  not  so 
soluble  as  calcium  chloride,  nor  is  it  leached  to  so  great  an 
extent.  Loss  of  calcium  from  soils  is  hence  not  so  great  as 
in  the  case  of  the  chloride. 

170.  Kainite. — This  fertilizer  was  formerly  the  mineral 
of  the  same  name,  the  formula  of  which  is  KCl.MgSO4.6H2O, 
but  at  present  it  is  merely  a  name  for  a  potash  fertilizer 
containing  12  per  cent,  potash,  the  form  of  the  potassium 
and  the  other  compounds  varying  considerably.  The  per- 
centage of  potash  only  is  constant.  Since  kainite  always 
contains  chlorine  in  some  form,  it  is  open  to  the  same 
objection  as  is  the  muriate  of  potash,  but  it  is  nevertheless 
a  good  low  grade  form  of  potash. 

171.  Wood  Ashes. — One  of  the  oldest  sources  of  potash  is 
wood  ashes.  When  clean,  hard  wood  is  carefully  burned,  the 
potash  content  may  run  up  to  8  or  10  per  cent.,  mostly  in  the 
carbonate  form.  In  addition  there  may  be  1  or  2  per  cent,  of 
phosphoric  acid,  and  30  per  cent,  of  calcium  compounds, 
the  calcium  being  in  the  oxide  form  when  freshly  burned, . 
but  changing  to  carbonate  on  exposure.  The  wood  ashes 
now  on  the  market  are  of  a  very  inferior  grade,  carrying 
not  more  than  3  or  4  per  cent,  of  potash  in  unleached  ashes. 
Leached  ashes,  that  is,  ashes  which  have  been  leached  to 
extract  potash  for  other  purposes  than  for  fertilizers,  or 
ashes  which  have  been  exposed  to  the  weather  and  leached 
by  rain,  contain  usually  less  than  1  per  cent,  potash. 

Potassium  carbonate  in  wood  ashes  is  a  good  fertilizer 
unless  too  much  is  applied,  when  it  has  a  deflocculating 
effect  on  soil  grains  and  is  poisonous  to  plants.  This  car- 
bonate and  the  calcium  carbonate  in  wood  ashes  are  both 
neutralizers  of  soil  acidity  and  are  valuable  for  this  purpose. 

172.  Natural  Brines. — Certain  lakes  in  Nebraska  and 
California  are  rich  in  potash  salts,  largely  carbonate,  but 
some  sulphate  and  chloride  as  well  as  similar  sodium  salts. 
The  water  from  these  lakes  is  evaporated.  The  dried  residue 
contains  20  to  30  per  cent.  K2O.  This  is  at  present  the 
largest  domestic  source  of  potash. 


222 


POTASH  FERTILIZERS 


173.  Kelp  and  Alunite. — The  giant  kelps  or  seaweeds 
on  the  Pacific  coast  (Fig.  55),  and  alunite,  a  mineral  found 
to  some  extent  in  Utah,  and  consisting  of  a  double  sul- 


=^^- 

J^K\  J 

P'Hl 

jK. 

111    . 

WM 

mBj^ 

iXs^^Wf-^i 

iKr^M 

l^ft 

Ng 

-      '  , : 

Fia.  55. — Giant  kelp. 

phate  of  potassium  and  aluminium,  are  also  important 
domestic  sources  of  potash.  The  giant  kelps  grow  rapidly 
and  sometimes  attain  a  length  of  hundreds  of  feet.     Dry, 


REFERENCES  223 

they  contain  15  to  20  per  cent,  potash  and  their  ashes 
contain  as  much  as  30  to  35  per  cent,  potash  in  the  form 
of  the  chloride.  Alunite  contains  10  per  cent,  potash, 
but  can  be  ignited  and  the  potash  content  increased  to  15 
per  cent.,  or  ignited  and  the  leeched  potassium  sulphate 
evaporated,  when  the  nearly  pure  potash  salt  can  be  obtained. 
The  latter  process,  however,  is  expensive.  Both  kelp  and 
alunite  have  given  good  results  as  a  fertilizer  with  no  treat- 
ment other  than  drying  in  the  case  of  kelp  and  pulverizing 
in  both  cases.  Used  in  this  way,  however,  they  are  low- 
grade  fertilizers. 

174.  Cement  Dust. — The  fine  dust  from  cement  works 
and  even  from  blast  furnaces  carries  2.5  to  9  per  cent.  K2O, 
which  is  slowly  available.  This  dust  can  be  used  just  as  it  is  or 
it  can  be  leached  and  a  high  grade  sulphate  obtained.  Although 
with  proper  appliances  for  collection  this  dust  can  be  our 
greatest  source  of  potash,  it  is  not  yet  used  to  any  great  extent. 

175.  Tobacco  Waste. — In  some  sections  of  the  country 
the  stems,  stalks,  and  other  waste  from  harvesting  the  crop 
and  manufacturing  tobacco  products,  can  be  obtained 
easily.  If  ground  fine  this  waste  makes  excellent  fertilizing 
material,  being  fairly  available.  The  potash  content  varies 
from  4  to  10  per  cent.,  phosphoric  acid  less  than  1  per  cent., 
and  nitrogen  from  2  to  4  per  cent.,  sometimes  as  much  as 
half  of  it  in  the  nitrate  form. 

EXERCISES 

1.  Suppose  a  soil  is  lacking  in  available  potassium  and  potash  fertilizers 
are  not  to  be  had,  state  in  detail  how  a  crop  of  potatoes  might  suffer. 

2.  Tabulate  all  the  fertilizers  that  are  immediately  available;  that  must 
undergo  nitrification;  that  leaves  the  soil  acid;  that  leave  it  basic;  that  will 
puddle  the  soil;  that  are  high  grade;  that  are  low  grade;  that  are  slaughter- 
house wastes;  that  can  be  made  by  the  use  of  electricity;  that  are  easUy 
leached;  that  are  easily  absorbed;  that  are  easily  adsorbed. 

3.  Compare  the  amounts  of  nitrogen,  phosphoric  acid  and  potash  in  the 
average  soil  and  in  the  film  water.  What  do  these  figures  indicate  as  to 
the  need  for  potash? 

4.  What  crops  remove  the  most  potash  per  acre? 

5.  If  potash  fertilizers  are  absorbed  in  the  soil,  into  what  compound 
might  the  potassium  be  changed?  write  equations.  What  conditions  would 
further  its  absorption? 

6.  What  property  studied  in  this  text  and  displayed  toward  potassium 
in  sea-water  is  developed  extremely  by  kelp? 

REFERENCES 
See  references  at  end  of  Chapter  VIII. 


CHAPTER  XII 
LIME 

Nitrogen,  phosphorus,  and  potassium  compounds  are 
direct  or  food  fertiUzers  primarily.  It  is  for  their  food  value 
to  the  plant  that  they  are  purchased.  Calcium  compounds, 
on  the  other  hand,  are  usually  considered  as  indirect  ferti- 
lizers or  amendments.  Calcium  is,  of  course,  an  essential 
element  in  the  growth  of  plants,  but  the  effects  of  compounds 
of  calcium  on  the  soil,  and  the  exploitation  of  these  effects 
has  given  calcium  an  importance  for  other  than  feeding 
purposes.  As  a  plant  food,  however,  calcium  is  frequently 
necessary  in  soils,  especially  for  certain  crops,  and  it  is 
necessary  to  consider  calcium  in  this  connection,  without 
at  all  minimizing  its  effect  as  an  amendment. 

176.  Calcium  Fertilizers  as  Plant  Food. — The  total  amount 
of  calcium  in  soils  of  course  varies  considerably,  but  on  the 
average  is  not  as  much  as  that  of  potassium — 0.5  to  1.50  per 
cent.  In  many  cases  it  may  be  present  in  part  as  calcium  car- 
bonate which  is  fairly  soluble  in  soil  moisture,  but  most  of 
it  is  in  silicate  and  organic  form  and  may  be  very  insoluble. 
Since  calcium  carbonate  is  so  soluble,  it  very  frequently 
happens  that  this  compound  is  entirely  lacking  even  in 
limestone  soils.  As  a  result,  soils  may  lack  sufficient  available 
calcium  for  the  nutrition  of  crops. 

Some  farm  crops  do  not  need  very  much  calcium,  it  is 
true,  but  other  crops  like  clover  and  alfalfa  do  need  large 
quantities.  Table  XII  shows  the  amount  of  calcium  oxide 
removed  by  various  crops.  Of  course,  this  represents  the 
amount  removed  only,  and  not  the  whole  amount  needed, 
for  plants  at  harvest  do  not  remove  as  much  as  they  need 
during  their  growth, 

(224) 


SOIL  ACIDITY  225 

Tablb  XII. — Amount  of  CaO  Removed  by  Variods  Crops 

(Expressed  in  pounds  per  acre.) 

Alfalfa 212 

Cabbage 96 

Corn 12 

Clover 90 

Oats •  .      .      .  11 

Potatoes 31 

Timothy 14 

Tobacco 83 

Wheat 8 

In  many  cases,  it  is  true,  sufficient  calcium  is  added  in 
the  ordinary  fertilizers  to  feed  crops.  Table  XIII  gives  the 
estimated  amount  of  calcium  oxide  in  100  pounds  of  various 
fertilizers. 

Table  XIII. — Amount  of  CaO  in  Various  Fertilizers 

Fertilizer.  Form  of  Calcium.  Per  cent.  CaO. 

Acid  phosphate  Phosphate  and  sulphate  .      .  .21 

Basic  slag  Phosphate,  silicate,  and  oxide  48 

Bone  meal  Phosphate 27 

Rock  phosphate  Phosphate  and  carbonate       ...     42 

Wood  ashes  Carbonate  and  phosphate      ...     34 

It  may  happen,  however,  that  a  fertilizer  application 
does  not  add  calcium  and  the  crop  becomes  starved  for  lack 
of  this  essential  element.  Particularly  may  this  be  true  in 
the  case  of  clover  and  alfalfa,  as  mentioned  above.  An 
application  of  lime,  then,  has  the  added  benefit  of  feeding 
the  crop. 

177.  Soil  Acidity. — One  of  the  most  important  effects  of 
adding  lime  to  the  soil  is  the  neutralization  of  soil  acidity — or 
to  "sweeten  a  sour  soil."  This  condition  in  the  soil  is  very 
common,  may  occur  in  all  kinds  of  soils,  and  in  fact  is  the 
natural  result  of  cropping.  Its  bad  effect  on  crops  is  fre- 
quently exaggerated,  some  crops  preferring  an  acid  soil  and 
even  refusing  to  grow  in  neutral  or  alkaline  soils.  For 
ordinary  crops,  however,  in  the  usual  farm  rotation,  a  soil 
which  is  neutral  or  slightly  alkaline  is  preferable  and  should 
be  maintained. 

The  primary  cause  of  soil  acidity  is  the  production  of 
acids  or  salts  that  are  acid  to  litmus.  These  acids  may  be 
organic  or  inorganic  in  nature  and  may  vary  in  their  harmful 
15 


226  LIME 

effect  on  crops.  They  may  occur  in  the  soil  as  a  result  of 
natural  changes  which  take  place  particularly  when  the  soil 
is  cultivaited  and  crops  grown,  or  they  may  be  the  result 
of  the  application  of  fertilizers,  in  which  case  soil  acidity 
may  be  said  to  be  caused  by  artificial  means.' 

(a)  Natural  Acidity. — ^When  organic  matter  in  the  soil 
undergoes  decomposition  through  bacterial  action,  organic 
acids  are  some  of  the  intermediate  products.  Decomposition 
in  the  presence  of  air  is  an  oxidation  process,  and  with 
thorough  aeration  results  ultimately  in  the  formation  of 
carbon  dioxide,  water,  and  inorganic  salts,  the  last  coming 
from  the  combination  of  mineral  elements  with  the  organic 
matter.  Nitric  acid,  of  course,  is  formed  from  nitrogenous 
compounds  and  possibly  mineral  acids,  but  before  complete 
oxidation  occurs,  and  especially  in  soils  not  thoroughly 
aerated,  organic  acids  are  formed.  These  acids  are  some- 
times fairly  simple,  like  acetic,  or  butyric,  or  oxalic,  but 
more  frequently  they  are  very  complex,  and  many  of  them 
unknown.  In  the  absence  of  air,  as  in  water-logged  soils, 
acids  are  even  more  commonly  produced  as  a  result  of 
what  may  be  called  intermolecular  oxidation,  where  one 
compound  is  oxidized  at  the  expense  of  another. 

Another  natural  cause  of  acids  is  the  removal  of  bases 
from  salts  by  plants  and  by  certain  hydrated  compounds 
in  the  soil.  Plant  root  hairs  exercise  a  so-called  "selective 
absorption"  in  taking  up  plant  foods  (Section  56).  Sulphates 
and  chlorides,  for  example,  are  split  up,  the  base  element 
entering  the  plant  and  the  acid  radical  being  left  in  the  soil 
as  an  acid.  Certain  colloidal  materials  like  hydrated 
silicates  and  humus  produce  this  same  result,  the  base 
being  adsorbed  or  perhaps  chemically  combined  with  the 
colloid.  It  is  possible  that  hydrolysis  takes  place  previous 
to  the  absortive  phenomenon.  This  means  the  formation  of 
a  hydroxide  and  an  acid,  thus : 

KCl  +  HOH  =  KOH  +  HCl. 

(6)  Artificial  Acidity. — ^The  application  of  ammonium 
sulphate  results  in  the  production  of  nitric  acid  from  the 
ammonia  by  the  nitrifying  bacteria,  and  of  sulphuric  acid 


SOIL  ACIDITY 


227 


as  the  residue  from  the  nitrification.    Figs.  56  and  57  show 
the  effect  of  such  acidity  on  corn  and  oats.    Figs.  58  and  59 


ri«r  2-   V\M\  tt^Anm  » 


|«»lfc*«*«l   l«  4VMLW  V«i.^| 


FICLU    T«AT«ENT 


Fig.  56. — Effect  of  acidity  resulting  from  use  of  ammonium  sulphate. 
Corn.  General  fertilizer  plats,  Department  of  Agronomy,  Pennsylvania 
Station. 


228 


LIME 


show  the  effect  of  the  same  treatment  on  corn  and  oats, 
but  in  soil  that  contains  enough  limestone  to  neutralize  the 
acidity.  Sulphate  and  particularly  the  muriate  of  potash 
also  tend  to  leave  an  acid  residue,  due  to  the  absorption  of 
potassium  by  plants  or  colloids  and  the  presence  of  the  acids 
sulphuric  and  hydrochloric.  This  of  course  is  the  same 
phenomenon  described  under  natural  acidity,  except  that 
it  is  more  pronounced. 


Fig.  57. — Effect  of  acidity  lesulling  from  use  of  ammonium  sulphate. 
Oats.  General  fertilizer  plats,  Department  of  Agronomy,  Pennsylvania 
Station. 


Whether  or  not  a  soil  becomes  acid  from  any  or  all  of  the 
above  mentioned  causes  depends  on  the  absence  or  presence 
of  sufficient  bases  to  neutralize  the  acids  as  they  are  formed. 
In  other  words  the  causes  above  enumerated  produce  acids. 
The  effect  is  noticed  if  insufficient  bases  are  present  to 
neutralize  the  acids  (Figs.  56,  57,  58,  and  59).  The  principal 
basic  material  in  the  soil  is  calcium  carbonate  resulting  from 
limestone  or  from  silicates  containing  calcium.    Soils  derived 


SOIL  ACIDITY 


229 


from  limestone  contain  particles  of  calcium  carbonate  which 
slowly  dissolve,  yielding  a  solution  which  neutralizes  any 
acids  resulting  from  organic  decomposition  or  selective 
absorption.     Little  calcium  is,  as  a  rule,  present  in  silicate 


fUt  M 


4«  IJ»  Hill  ••  i»*  "^^  »^»- 

IMlk  IkjO  ••  •-•  •<    I"'-* 
,aa4    lHXvl»*w  *«•»••*>>'•■**-■*"' 


mMmI  U 


Fig.  58. — EfToet  of  sufficient  limestone  in  the  soil  to  neutralize  the  acitiity 
from  ammonium  sulphate.  Corn.  General  fertilizer  plats,  Department  of 
Agronomy,  Pennsylvania  Station. 

form  and  hence  little  carbonate  can  be  produced  from  this 
source.  In  time  all  the  calcium  carbonate  is  dissolved  out 
and  then  the  acid  condition  of  the  soil  asserts  itself.  This 
solution  of  calcium  carbonate  takes  place  rapidly  and 
completely. 


230 


LIME 


On  the  other  hand,  it  frequently  happens  that  soils  derived 
from  silicate  rocks  containing  calcium  do  not  become  acid 
readily.  This  is  because  the  calcium  is  slowly  dissolved 
out  as  calcium  bicarbonate  and  but  little  is  wasted  due  to 
leaching.  Practically  all  of  it  neutralizes  acids  or  serves 
some  other  valuable  function.  There  is  no  excess  at  any 
one  time  and,  moreover,  the  total  amount  of  calcium  present 
is  very  considerable. 


Fio.  59. — Effect  of  sufficient  limestone  in  the  soil  to  neutralize  the  acidity 
from  ammonium  sulphate.  Oats.  General  fertilizer  plats,  Department  of 
Agronomy,  Pennsylvania  Station. 


But,  nevertheless,  the  general  tendency  of  all  soils  is  to 
lose  the  basic  material  and  to  produce  acids  from  various 
causes.  This  combination  of  changes  results  in  an  acid  or 
sour  soil. 

Virgin  soils  may  be  temporarily  acid,  the  latter  being 
caused  by  the  accumulation  of  organic  matter.  Cultivation 
will  cause  further  oxidation  and  destruction  of  these  acids 
and  also  will  cause  increased  solution  of  basic  material  and 
hence  neutralization  of  the  acids. 


LIME 


231 


But  whatever  the  cause  may  be,  permanent  soil  acid,  as 
a  rule,  should  be  neutralized  by  certain  calcium  compounds, 
loosely  called  "lime." 

178.  Lilne. — The  chemical  term  lime  is  used  for  calcium 
oxide,  CaO.  Agriculturally,  however,  lime  is  any  compound 
of  calcium  which  will  neutralize  acids.  The  compounds 
having  this  power  are  the  carbonate,  hydroxide,  and  oxide. 


km-mm 


Fig.  60. — Limestone  quarry.     Department  of  Experimental  Agricultural 
Chemistry,  Pennsylvania  Station. 

(a)  Calcium  Carbonate,  CaCOs. — This  form  of  calcium 
occurs  in  limestone,  oyster  shells,  shell  marl,  and  chalk, 
all  of  which  may  contain  as  much  as  95  to  98  per  cent, 
calcium  carbonate,  but  frequently  contain  less  (Fig.  60 
shows  a  limestone  quarry).  Limestone  very  often  is  com- 
posed of  magnesium  carbonate  as  well  as  calcium  carbo- 
nate, in  amounts  varying  from  a  few  per  cent,  up  to  45 
per  cent.  When  the  latter  content  of  magnesium  carbo- 
nate is  present  the  mineral  is  called  dolomite.  To  be  used 
on  the  soil  all  forms  of  calcium  carbonate  should  be  ground 
very  fine,  preferably  so  that  75  per  cent,  at  least  passes  a 
hundred  mesh  sieve.    It  must  be  remembered  that  it  is  the 


232 


LIME 


calcium  oxide  content  only  which  is  of  value  in  neutralizing 
acids.  One  hundred  pounds  of  calcium  carbonate  contain 
fifty-six  pounds  of  calcium  oxide,  or  to  be  more  in  accord 
with  the  naturally  occurring  limestones,  one  hundred  pounds 
of  95  per  cent,  limestone  contain  fifty-three  pounds  of 
calcium  oxide. 


Fig.  61. — Lime  kilns.     Department  of  Experimental  Agricultural  Chem- 
istry, Pennsylvania  Station. 

(6)  Calcium  Oxide,  called  also  Burnt  Lime,  Stone  Lime, 
Lump  Lime,  Rock  Lime,  Caustic  Lime,  and  Quicklime, 
CaO. — This  is  prepared  from  any  of  the  forms  of  calcium 
carbonate,  although  usually  from  limestone,  by  "burning," 
either  in  specially  built  kilns  (Fig.  61)  or  in  piles  in  the  field. 
In  either  case  the  limestone  is  alternated  with  wood  or  coal 
and  the  latter  by  burning  produces  sufficient  heat  to  drive 
off  carbon  dioxide  from  the  limestone  and  leave  calcium 
oxide,  thus: 

CaCOs  +  heat  =  CaO  +  CO2.        * 

If  pure  this  form  of  lime  is  all  valuable  in  neutralizing  acids 
and  is  the  most  concentrated  form  that  can  be  obtained. 


AVAILABILITY  OF  LIME  233 

It  is  in  fact  the  only  fertilizer  which  contains  practically 
100  per  cent,  of  the  valuable  constituent. 

(c)  Calcium  Hydroxide,  Slaked  Lime,  Hydrated  Lime, 
Ca(0H)2. — When  water  is  added  to  a  lump  of  calcium  oxide 
it  swells,  gives  off  heat,  and  finally  crumbles  to  a  fine,  dry 
powder.  The  process  is  called  "slaking,"  and  the  product, 
slaked  lime.    The  reaction  is  expressed  thus: 

CaO+H20  =  Ca(OH)j. 

The  volume  of  the  calcium  oxide  is  increased  two  or  three 
times,  and  the  weight  is  increased  one-third.  To  put  it  in 
another  way,  100  pounds  of  slaked  lime  contain  about  75 
pounds  of  calcium  oxide.  A  solution  of  calcium  hydroxide 
in  water  is  called  lime  water.  A  thin  paste  of  the  hydroxide 
and  water  is  called  milk  of  lime. 

(d)  Air-slaked  Lime. — When  burnt  lime  is  allowed  to 
remain  exposed  to  the  air  it  first  takes  on  water  and  then 
carbon  dioxide  until  it  finally  becomes  calcium  carbonate, 
thus : 

CaO  +  H2O  =  Ca(0H)2. 
Ca(0H)2  +  CO2  =  CaCO.  +  H2O. 

A  pile  of  burnt  lime  slakes  first  on  the  outside  and  the 
lumps  fall  apart  covering  the  pile  with  fine  material  and 
filling  up  the  interstices  so  as  to  protect  the  interior  of  the 
pile  from  rapid  change  to  carbonate  (Fig.  62).  The  outside 
changes  very  quickly  to  the  carbonate.  Without  a  chemical 
analysis  it  would  be  impossible  to  tell  how  much  calcium 
oxide  there  is  in  a  given  lot  of  air-slaked  lime,  unless,  of  course, 
the  amount  of  burnt  lime  originally  present  is  known.  The 
process,  however,  is  very  slow.  For  example,  a  sample 
taken  at  a  depth  of  4  inches  from  the  surface  of  a  heap 
exposed  ten  years  contained  27  per  cent,  calcium  carbonate 
and  37  per  cent,  calcium  hydroxide. 

179.  Availability  of  Lime. — Under  the  best  conditions 
chemically  pure  calcium  oxide  is  soluble  as  calcium  hydroxide 
at  ordinary  temperatures  to  the  extent  of  one  part  in  1000 
parts  of  pure  water.  Chemically  pure  calcium  carbonate, 
freshly  precipitated,  is  very  slightly  soluble  in  pure  water. 


234 


LIME 


but  in  water  saturated  with  carbon  dioxide  at  ordinary 
temperature  it  is  soluble  as  calcium  bicarbonate  to  the 
extent  of  one  part  in  about  1000  parts.  The  less  carbon 
dioxide  present,  the  less  calcium  carbonate  is  dissolved.  Soil 
moisture  contains  small  quantities  of  carbon  dioxide.  This 
would  change  calcium  hydroxide  dissolved  in  it  to  carbonate, 
a  change  which  takes  place  very  quickly.  Further  quantities 
of  carbon  dioxide  would  change  the  carbonate  to  bicarbonate 
and  so  dissolve  it.  Since  carbon  dioxide  is  being  constantly 
produced  in  the  soil,  the  change  of  hydroxide  to  carbonate 
and  bicarbonate  is  fairly  rapid.    On  account  of  this  double 


Fig.  62. — Pile  of  air-slaked  lime.    (Hibshman.) 

change  of  hydroxide,  it  makes  very  little  difference  which 
form  is  used  on  soils,  whether  fresh  slaked  lime,  air-slaked 
lime,  or  limestone.  Burnt  lime  has  a  caustic  effect  on  plant 
growth,  and  is  said  to  cause  rapid  decay  of  organic  matter 
in  the  soil;  consequently  it  should  be  used  with  great  care  and 
never  should  be  applied  near  seeding  time.  Because  of  a 
difference  in  physical  condition,  or  more  accurately  stated, 
because  of  a  difference  in  molecular  arrangement,  there  is 
a  difference  in  the  solubility  of  various  carbonates.  Shell 
marl,  oyster  shells,  limestone,  is  the  order  of  solubility  of 
these  carbonates.  For  practical  purposes,  however,  it  may 
be  said  again  that  the  availability  of  all  forms  of  lime  is 


EFFECT  OF  LIME  ON  THE  SOIL 


235 


about  the  same.  In  other  words  the  farmer  may  apply 
slaked  lime,  air-slaked  lime,  or  ground  carbonate  in  the  form 
of  shell  marl,  oyster  shells,  or  limestone,  with  equally  good 
results.  It  is  the  bicarbonate  of  lime  in  any  event  which 
is  the  active  form  in  the  soil.  All  that  he  must  remember 
is  that  to  get  100  pounds  of  calcium  oxide  he  must  use  100 
pounds  of  burnt  lime,  130  pounds  of  slaked  lime,  or  180 
pounds  of  carbonate;  of  air-slaked  lime  he  must  know  the 
calcium  oxide  content. 


Fig.  63. — Lime  and  clover  test.     Check  plat,  yield  of  hay  980  pounds  per 
acre.     Pennsylvania  Station. 


180.  Effect  of  Lime  on  the  Soil. — Inasmuch  as  lime  is 
for  the  most  part  a  soil  amendment,  the  changes  which  it 
occasions  in  the  soil,  and  by  which  plants  are  benefited, 
are  of  great  importance.  No  other  element  has  such  a  great 
variety  of  uses  in  crop  production,  and  yet  it  must  not  be 
considered  a  universal  panacea  for  all  soil  ills.  Figs.  63,  64, 
65,  and  66  show  that  while  lime  is  needed  to  correct  acidity, 
fertilizers  also  are  needed. 

(a)  Neutralizing  Acids. — ^This  is  perhaps  the  best  known 
function  of  lime,  and  the  results  are  far  reaching.  Many 
acids  are  poisonous  to  plants.  That  is,  there  is  a  direct 
physiological  effect,  more  particularly  from  the  mineral 
acids  and  from  some  organic  acids,  oxalic  for  example.  Then 


236 


LIME 


again,  acids  check  the  activity  of  soil  bacteria.  Decompo- 
sition is  prevented.  This  means  that  the  production  of 
carbon    dioxide    is    limited,   and    hence,   solution    of    soil 


Fig.  64. — Lime  and  clover  test.     Lime  at  rate  of   1000  pounds  per  acre. 
Yield,  1960  pounds.    Pennsylvania  Station. 


Fig.  65. — Lime  and  clover  test.     Commercial  fertilizer  only  at  rate  of  250 
pounds  per  acre.    Yield,  1560  pounds.     Pennsylvania  Station. 

minerals  is  lessened  and  plant  food  thereby  diminished. 
Ammonification  and  nitrification  are  very  seriously  checked 
by  acids  and  the  supply  of  nitrogen  for  plants  is  therefore 
cut  off.     The  activity  of  nitrogen-fixing  bacteria  is  also 


EFFECT  OF  LIME  ON   THE  SOIL 


237 


lessened  by  acids.     Fig.  67  shows  the  effect  of  different 
amounts  of  lime  on  the  growth  of  clover  in  an  acid  soil. 


Fig.  66. — Lime  and  clover  test.     Lime  and  fertilizer.     Same  amounts  as 
,     before.    Yield,  2526  pounds  per  acre.     Pennsylvania  Station. 


Fig.  67. — Pot  test  of  lime  on  clover  in  acid  soil.  Amounts  indicated  are 
rates  per  acre,  5200  pounds  CaCOa  being  needed  to  neutralize  the  soil 
according  to  the  Veitch  method.  Yields  from  left  to  right:  8.7  gms.;  8.8 
gms.;  7.9  gms.;  2.3  gms.;  0  gms.  Department  of  Agronomy,  Pennsylvania 
Station. 


By   neutralizing   soil   acids   lime   prevents   poisoning   of 
plants,  hastens  decomposition  of  organic  matter,  and  in- 


238  LIME 

creases  nitrification  and  fixation.  The  fact  that  lime  hastens 
decomposition  is  frequently  charged  against  it.  This  is  a 
great  mistake,  for  decomposing  organic  matter  is  of  very 
great  value  to  crops  and  should  be  encouraged,  within 
reason  of  course.  Active  organic  matter  helps  to  release 
the  stores  of  unavailable  plant  food.  Organic  matter  in  the 
soil  should  be  maintained  so  that  it  may  be  destroyed.  A 
mere  piling  up  of  organic  matter  in  the  soil,  organic  matter 
that  does  not  decay,  is  useless  except  for  holding  moisture 
and  improving  soil  structure. 

(6)  IVIaking  Potassium  Available. — Lime  is  said  to 
release  potassium  from  insoluble  silicates  and  humates,  cal- 
cium taking  the  place  of  potassium  in  these  compounds  and 
potassium  being  made  soluble  as  the  carbonate.  There 
seems  to  be  evidence  now,  however,  which  indicates  con- 
siderable doubt  as  to  the  ability  of  lime  to  make  potash 
available. 

(c)  Making  Phosphorus  Available. — Lime  also  changes 
iron  and  aluminium  phosphates  to  calcium  phosphate  and 
thereby  makes  the  phosphorus  compound  soluble  in  the  soil 
moisture  (Section  129,  a).  Also  by  maintaining  a  supply 
of  lime  in  the  soil,  phosphate  fertilizers  are  prevented  from 
changing  to  iron  and  aluminium  phosphates. 

It  must  be  borne  in  mind  that  valuable  as  lime  is  in  free- 
ing unavailable  potassium  and  phosphorus,  it  does  not  add 
either  of  these  elements  to  the  soil;  it  rather  exhausts  the 
soil.  This  is  of  course  beneficial — the  freeing  of  plant  food 
in  the  soil — but  additions  must  be  made  in  the  form  of 
phosphate  fertilizers  if  the  supply  is  to  be  maintained. 

(d)  Improving  the  Physical  Condition. — Lime  also  im- 
proves the  structure  of  soils  by  flocculating  heavy  clays  and 
binding  together  loose,  sandy  soils. 

(e)  Checking  Plant  Diseases. — Lime  destroys  some  fun- 
gous diseases  of  plants,  notably  the  club-root  or  finger-and- 
toe  disease  of  cabbage  and  turnips. 

(/)  Harmful  Effects. — Lime,  on  the  other  hand>  is  favor- 
able to  potato  scab.  It  prevents  the  growth  of  such  crops  as 
the  cranberry,  watermelon,  blueberry,  and  trailing  arbutus. 
It  is  not  known  why  this  is,  whether  they  can  live  better 


WASTE  LIME  239 

on  other  forms  of  calcium  than  the  bicarbonate  or  whether 
they  prefer  an  acid  soil.  Too  heavy  applications  of  caustic 
or  burnt  lime  particularly  destroy  organic  matter  to  an 
unreasonable  extent,  and  also  will  injure  germinating  seeds 
if  applied  too  near  to  seeding. 

181.  Use  of  Magnesian  Lime. — Some  limestones  contain 
magnesium,  and  small  amounts  do  no  harm.  Large  amounts 
up  to  45  per  cent,  (dolomite)  are  questionable.  When  burned, 
such  a  lime  slakes  with  difficulty,  and  may  cause  serious 
harm  to  crops  if  the  soil  to  which  it  is  applied  contains  an 
undue  proportion  of  magnesium.  Just  what  this  proportion 
should  be  varies  with  the  crop  and  depends  of  course  also 
on  the  relative  amounts  of  calcium  and  magnesium  that  are 
dissolved  in  the  soil  moisture.  On  the  other  hand,  magnesian 
lime  does  no  harm  on  soils  not  so  well  supplied  with  mag- 
nesium. To  be  safe  it  is  better  to  use  a  grade  of  lime  high  in 
calcium  carbonate. 

182.  Calcium  Sulphate,  Gypsum,  Land  Plaster,  CaS04.2H20. 
— ^This  material  is  used  to  some  extent  on  soils  as  an  amend- 
ment. It  frees  potassium  and  phosphorus  from  insoluble 
compounds,  and  is  said  to  hasten  the  decomposition  of 
organic  matter,  but  it  has  no  neutralizing  effect  and  is  not 
of  much  value.  The  other  compounds  of  calcium  have  all 
these  effects  plus  the  neutralizing  effect. 

183.  Waste  Lime. — Lime  is  used  in  purifying  coal  gas  and 
in  the  manufacture  of  sugar  from  beets.  Gas-lime  should 
be  exposed  to  the  air  for  some  time  before  applying  to  the 
soil,  or  should  be  added  to  the  soil  a  long  time  before  seeding 
because  it  contains  sulphides  and  sulphites  from  sulphur 
compounds  absorbed  from  the  gas.  These  compounds 
change  to  sulphates  on  exposure  to  the  air  and  are  thus 
rendered  harmless  to  plants. 

Lime  is  a  waste  product  in  the  manufacture  of  acetylene 
gas,  and  should  be  exposed  to  the  air  before  use  to  allow 
the  escape  of  traces  of  acetylene  which  is  harmful  to  seeds. 

Lime  from  these  processes  is  usually  a  mixture  of  hydroxide 
and  carbonate  and  is  valuable  for  agricultural  purposes  if 
it  can  be  obtained  cheap  and  if  the  content  of  calcium 
oxide  is  known. 


240  REFERENCES 

EXERCISES 

1.  Is  it  better  to  use  sodium  nitrate,  basic  slag  and  wood  ashes  on  an 
acid  soil,  or  ammonium  sulphate,  acid  phosphate  and  muriate  of  potash 
with  lime  in  a  rotation?     Why? 

2.  Prove  by  calculation  that  100  pounds  of  burnt  lime  are  equivalent 
to  130  pounds  of  slaked  lime,  and  180  pounds  of  carbonate. 

3.  In  order  of  importance  tabulate  all  the  functions  of  lime.  State  why 
you  have  placed  them  in  this  order. 

4.  On  an  acid  soil,  what  crops  would  suffer  most?  Why  would  they 
suffer? 

5.  Suppose  you  had  a  soil  which  turned  litmus  paper  red,  would  not  grow 
clover,  did  not  respond  to  an  application  of  lime,  what  treatment  would 
you  give  it? 

6.  Show  by  equation  what  happens  when  limestone  is  burned;  when  the 
resultant  product  is  left  piled  exposed  to  the  weather;  when  it  is  put  in  the 
soil  as  an  amendment. 

7.  Does  carbonic  acid  make  a  soil  acid?     Why? 

8.  Under  what  conditions  are  the  forms  of  lime  of  equal  merit? 

9.  What  different  compounds  of  the  same  elements,  other  than  the 
forms  of  calcium  carbonate,  show  a  difference  in  solubility? 

10.  Which  has  the  greater  neutralizing  power,  100  per  cent,  limestone 
or  a  mixture  of  70  per  cent,  calcium  carbonate  and  30  per  cent,  magnesium 
carbonate?     Which  would  you  apply  to  an  acid  soil?     Why? 

REFERENCES 

Penna.  Agr.  Expt.  Sta.  Report,  1899-1900,  Pt.  II,  p.  15.  The  Agricul- 
tural Use  of  Lime. 

Van  Slyke.     Fertilizers  and  Crops. 
Wheeler.     Manures  and  Fertilizers. 


CHAPTER  XIII 
FARM  MANURE 

Up  to  the  present  time  the  fertilizers  discussed  have  been 
commercial  products  only,  and  many  of  them  inorganic 
materials  of  value  only  for  the  plant  food  which  they  con- 
tain. There  is  one  fertilizer,  however,  which  is  produced  to  a 
greater  or  less  extent  on  every  farm,  and  which  contains 
not  only  the  three  principal  plant  foods,  but  which  also 
contains  organic  matter  and  bacteria,  both  of  which  are 
valuable  to  the  soil.  This  material  is  the  excrement  of 
domestic  animals  mixed  with  straw  or  other  litter.  In  this 
discussion  the  term  farm  manure  will  be  used  to  describe 
the  mixture  of  solid  and  liquid  excrement  of  any  domestic 
animal  with  the  litter  of  whatever  character.  There  is 
some  tendency  today  to  call  the  mixture  of  horse  excrement 
and  litter,  stable  manure;  and  cattle  excrement  with  litter, 
barnyard  manure.  The  term  manure  is  sometimes  applied 
to  any  fertilizing  material,  but  this  practice  is  more  common 
in  England  than  in  the  United  States. 

184.  Solid  Excrement. — ^The  solid  excrement,  or  feces, 
of  an  animal  are  the  undigested  portions  of  the  food.  This 
material  has  been  rather  thoroughly  comminuted  by  the 
animal  in  the  various  processes  of  mastication,  remastication 
in  the  case  of  ruminants,  and  of  churning  movements  in  the 
stomach  and  intestines.  On  account  of  the  more  complete 
mastication  and  digestion  in  cattle,  the  feces  of  the  latter 
are  more  finely  divided  and  more  compact  than  those  of 
horses.  Although  the  constituents  of  the  feces  have  not 
been  digested  and  absorbed  by  the  animal,  more  or  less 
decomposition  has  taken  place,  particularly  in  the  case  of 
the  proteins.  Part  of  this  change  has  occurred  in  the  stomach 
and  intestines  because  of  partial  enz\Tne  action,  and  part 
16  '  (241) 


242 


FARM  MANURE 


in  the  intestines  due  to  bacteria.  These  bacteria  are  present 
in  very  large  numbers  in  the  voided  excrement  and  are 
valuable  in  promoting  further  decomposition  in  the  soil. 
Although  on  this  account  feces  contain  plant  food  that  is 
more  available  than  it  was  in  the  original  animal  food,  never- 
theless, it  is  not  a  quick  acting  fertilizer.  All  of  the  fertil- 
izing constituents  in  feces  have  to  undergo  decomposition 
to  be  soluble  and  available  to  plants. 

The  amount  of  the  various  fertilizer  ingredients  in  solid 
excrement  varies  with  different  animals.  Table  XIV  gives 
the  average  percentage  composition  of  the  excrement  of  the 
common  farm  animals,  horse,  cow,  pig,  sheep,  and  hen. 
The  table  also  gives  the  amount  voided  per  year  for  each 
animal,  taking  the  indicated  weights  as  rough  averages. 

Table  XIV. — Composition  and  Amount  of  Animal  Excbbment 


Excrement. 

Nitrogen 
per  cent. 

Phosphoric 

acid 

per  cent. 

Kind  of 

animal  and 

average 

weight. 

Kind. 

Proportion 
per  cent. 

Amount 
voided  per 
year,  pounds 
per  average 

animal. 

Potash 
per  cent. 

Horse,  1300 

pounds 
Cow,  950 

pounds 
Pig,  150 

pounds 
Sheep,  120 

pounds 
Hen,  4 

pounds 

Solid 

Liquid 

Solid 

Liquid 

Solid 

Liquid 

Solid 

Liquid 

80 
20 
70 
30 
60 
40 
67 
33 

18,700 

4,700 

18,000 

7,600 

2,700 

1,800 

1,000 

500 

35 

0.55 
1.35 
0.40 
1.00 
0.55 
0.40 
0.75 
1.35 
1.00 

0.30 
Trace 
0.20 
Trace 
0.50 
0.10 
0.50 
0.05 
0.80 

0.40 
1.25 
0.10 
1.35 
0.40 
0.45 
0.45 
2.10 
0.40 

It  is  to  be  noted  that  the  solid  excrement  of  the  horse  is 
much  drier  than  that  of  the  cow,  hence  its  decomposition 
is  more  rapid  and  the  temperature  of  the  mass  rises  very 
considerably.  This  fact  is  made  use  of  in  making  "hot- 
frames"  in  the  early  spring.  Fermenting  horse  manure  is 
the  source  of  heat. 

185.  Liquid  Excrement. — ^The  liquid  excrement,  or  urine, 
of  animals  contains  waste  food  material  which  has  been 


LITTER  243 

digested  and  absorbed,  but  which  has  also  been  utilized, 
broken  down,  and  eliminated.  All  of  the  material  is  soluble 
and  is  quickly  made  available.  Decomposition  to  inorganic 
forms  of  plant  food  is  rapid.  Table  XIV  also  shows  the 
relative  amounts  of  liquid  excrement. 

186.  Litter. — By  litter  is  meant  the  plant  residues  or 
other  materials  used  in  stalls  as  bedding  for  animals  and 
which  becomes  mixed  with  excrement.  As  a  part  of  farm 
manure  litter  serves  important  functions,  such  as  the  ab- 
sorption of  urine,  and  of  ammonia  which  escapes  from  ex- 
crement on  decomposition.  It  also  makes  manure  easier 
to  handle  and  adds  organic  matter  and  plant  food. 

Table  XV  shows  the  number  of  pounds  of  water  and 
ammonia  absorbed  per  100  pounds  of  litter  of  various  kinds. 

Table  XV. — Amount  of  Water  and  Ammonia  Absorbed  by 
Litter 

Water         Ammonia 
pounds  per    pounds  per 
Kind  of  litter.  100.  100. 

Wheat  Straw 220  0.17 

Partly  decomposed  oak  leaves     ....  162  .... 

Pine  sawdust 435  0.05 

Peat 600  1.10 

Peatmoss          1300  0.86 

Table  XVI. — Composition  of  Litter 

Nitrogen       Phosphoric  acid         Potash 
Kind  of  litter.  per  cent.  per  cent.  per  cent. 

Straw 0.50  0.25  1.10 

Leaves 0.80  0.30  0.30 

Sawdust 0.45  0.30  0.70 

Peatmoss        ....  0.80  0.10  0.17 

Peat 0.85  0.18  0.08 

Table  XVI  shows  the  composition  of  various  litters  in  the 
fertilizing  constituents.  It  is  to  be  noted  that  straw,  the 
usual  form  of  litter,  contains  about  as  much  nitrogen,  phos- 
phoric acid,  and  potash  as  does  excrement,  so  that  as  far 
as  actual  plant  food  is  concerned  there  is  no  dilution  of  the 
amount  present  in  excrement  by  mixing  it  with  the  litter. 
Sawdust  and  shavings,  however,  which  are  used  to  a  con- 
siderable extent  in  cities,  contain  much  less  plant  food, 
and  furthermore,  they  decompose  very  slowly  in  the  soil, 


244  FARM  MANURE 

SO  that  what  plant  food  they  do  contain  becomes  available 
to  a  very  slight  extent.  But  sawdust  and  shavings  are  good 
absorbers  of  liquid,  even  better  than  straw,  and  are  con- 
sequently of  considerable  value.  They  do  no  harm  in  the 
soil  as  is  sometimes  claimed. 

187.  Mixed  Excrement. — Considering  the  mixture  of  solid 
and  liquid  excrement,  exclusive  of  litter,  it  is  found  that 
the  composition  varies  with  the  age  of  the  animal  and  the 
kind  of  food  eaten.  An  adult  animal,  working  or  fattening, 
retains  not  more  than  5  or  10  per  cent,  of  the  nitrogen, 
phosphoric  acid,  and  potash  in  the  food.  Cows  giving 
milk,  and  young  animals,  retain  from  25  to  50  per  cent,  of 
these  constituents  in  their  food.  Taking  the  average  excre- 
ment produced  on  the  farm,  it  may  be  said  to  contain 
about  80  per  cent,  of  the  fertilizing  constituents  of  the 
food  eaten. 

The  kind  of  food  eaten  will  influence  the  composition 
of  excrement.  If  the  food  consists  of  press  cake,  grains, 
bran,  or  other  concentrated  material,  the  excrement  will 
be  much  higher  in  nitrogen,  phosphoric  acid,  and  potash 
than  if  the  food  were  roughage,  or  ensilage,  or  beets  (see 
Table  III). 

188.  Farm  Manure. — This  product,  as  mentioned  at  the 
beginning  of  the  chapter,  is  a  mixture  of  solid  excrement, 
liquid  excrement,  and  litter.  As  can  be  readily  seen  from 
what  has  been  said  about  the  causes  of  variation  in  the 
composition  of  excrement,  and  what  is  known  about  variation 
in  the  composition  of  litters,  the  amount  of  plant  food  in 
farm  manure  is  never  constant.  From  the  discussion  which 
follows  as  to  the  decomposition  and  losses  of  manure  piles, 
it  is  to  be  noted  that  these  factors  also  affect  the  com- 
position. For  purposes  of  rough  calculation,  however,  it  is 
somewhat  generally  agreed  that  the  average  farm  manure 
contains  about  0.5  per  cent,  nitrogen,  0.25  per  cent,  phos- 
phoric acid,  and  0.5  per  cent,  potash;  or,  to  put  it  more 
plainly,  a  ton  of  farm  manure  contains  10  pounds  of  nitrogen, 
5  pounds  of  phosphoric  acid,  and  10  pounds  of  potash. 

189.  Compounds  in  Fresh  Farm  Manure. — When  first 
produced,  farm  manure  contains  in  the  solid  excrement, 


DECOMPOSITION  OF  FARM  MANURE  245 

starch,  cellulose,  other  carbohydrates,  lignin,  fat,  proteins 
in  various  stages  of  decomposition,  mineral  elements  com- 
bined organically,  remains  of  intestinal  juices,  and  other 
compounds.  The  liquid  portion  contains  organic  and  in- 
organic salts,  soluble  nitrogenous  compounds  like  urea,  etc. 
The  litter,  of  course,  contains  the  usual  plant  compounds 
present  in  such  materials. 

190.  Bacteria  in  Manure. — Liquid  excrement  when  first 
voided  contains  no  bacteria,  but  the  solid  excrement  con- 
tains exceedingly  large  numbers,  determinations  on  various 
excrements  showing  from  90,000,000  to  150,000,000  organisms 
in  one  gram  of  material.  In  addition  to  this,  litter  contains 
from  10,000,000  to  400,000,000  organisms.  In  the  course 
of  time  the  number  of  organisms  diminishes  as  food  becomes 
scarcer  and  the  products  of  their  activities  increase  sufficiently 
to  kill  many  of  them. 

191.  Decomposition  of  Farm  Manure. — As  a  result  of  its 
high  bacterial  content,  manure  commences  to  decompose  as 
soon  as  it  is  produced.  Molds  also  help  the  decomposition. 
The  bacterial  changes  which  take  place  in  it  are  of  consider- 
able importance  and  can  be  discussed  best  under  two  heads: 
Aerobic,  where  air  has  free  access  to  the  materials;  and 
anaerobic,  where  air  is  kept  out. 

(a)  Aerobic. — ^The  most  important  changes  taking  place 
in  manure  are  those  affecting  nitrogen.  This  element  is 
present  in  the  urine  largely  as  urea,  CO(XH2)2,  which  is 
attacked  very  easily  by  several  kinds  of  bacteria.  The 
action  is  one  of  hydrolysis,  thus : 

CO(NH2)2  +  2H2O  =  (NHOsCO,. 

The  ammonium  carbonate  readily  breaks  up  on  exposure 
to  the  air,  as  follows: 

(NH4)2CO,^2NH,  +  CO2  +  H2O. 

This  results,  of  course,  in  loss  of  nitrogen,  for  the  ammonia 
escapes  into  the  air.  The  reaction  is  reversible,  and  in  the 
presence  of  plenty  of  carbon  dioxide  and  water  with  no 
circulation  of  air  to  remove  the  volatile  products,  ammonium 
carbonate  is  not  decomposed. 


246  FARM  MANURE 

In  the  solid  excrement  nitrogen  is  present  in  protein 
forms  which  have  resisted  decomposition  in  the  digestive 
tract  of  the  animal,  and  hence  do  not  decompose  very  rapidly 
in  manure.  In  the  litter  the  nitrogenous  compounds  are  also 
proteins,  and  although  somewhat  more  easily  broken  down 
than  the  proteins  of  the  solid  excrement,  they  are  not  decom- 
posed very  rapidly.  Considering  the  nitrogen  compounds  in 
the  solid  part  of  the  manure,  it  can  be  said  that  they  break 
down  in  the  presence  of  air  with  the  formation  of  ammonia 
which  escapes  into  the  atmosphere.  Moreover,  in  the 
presence  of  plenty  of  air,  ammonia  is  further  oxidized  to 
free  nitrogen.  True  nitrification,  that  is,  the  formation  of 
nitrates,  is  not  a  common  bacterial  change  in  manure  piles. 

Aerobic  decomposition  results  in  a  gradual  change  of 
carbohydrates — cellulose,  starch,  and  pentosans — and  of  fats, 
as  well  as  of  proteins,  to  carbon  dioxide  and  water,  with 
the  intermediate  production  of  organic  acids.  Compounds 
containing  potassium  and  other  bases  decompose  with  the 
formation  of  carbonates  of  the  bases.  Phosphorus  and 
sulphur  in  proteins  remain  as  phosphates  and  sulphates, 
or  more  correctly  speaking  as  phosphoric  and  sulphuric 
acids  which  are  neutralized  by  the  bases  present.  As  a 
matter  of  fact,  there  is  an  excess  of  alkaline  carbonates  in 
decomposing  manure  piles,  whether  the  action  is  aerobic 
or  anaerobic.  This  is  evidenced  by  the  dark  liquids  which 
may  be  seen  draining  from  manure  piles.  This  dark  liquid 
is  an  alkaline  extract  of  humus,  for  humus,  or  at  least  humus- 
like compounds,  result  from  partial  decomposition  of  the 
organic  matter,  more  particularly  where  there  is  not  much 
air  present. 

In  general,  aerobic  decomposition  of  manure  results  in  the 
production  of  considerable  heat.  Horse  and  sheep  manure 
being  more  porous  and  drier,  decompose  very  easily  and 
are  called  "hot"  manures.  The  manure  of  pigs  and  cattle, 
on  the  other  hand,  are  more  compact,  contain  more  water, 
and  hence  do  not  decompose  so  rapidly.  They  are  called 
"cold"  manures.  The  loss  of  carbon  dioxide  and  water  from 
manure,  of  course,  results  in  loss  of  weight. 


LOSS  247 

(6)  Anaerobic. — When  air  is  not  present  in  manure, 
decomposition  and  loss  of  ammonia  are  not  so  rapid.  While 
urea  may  change  to  ammonium  carbonate  there  is  no  op- 
portunity for  this  compound  to  break  up  into  ammonia, 
carbon  dioxide,  and  water.  The  proteins  of  the  soHd  portion 
are  slowly  changed  to  soluble  compounds  and  some  ammonia, 
but  the  latter  is  not  lost  to  any  great  extent.  Moreover, 
much  of  the  nitrogen  so  changed  is  absorbed  by  the  bacteria 
themselves  and  retained  in  the  manure  as  insoluble  com- 
pounds. 

The  non-nitrogenous  portions  of  the  manure  are  broken 
down  into  organic  acids,  carbon  dioxide  to  some  extent,  and 
in  addition  considerable  quantities  of  hydrogen  and  methane. 
Sulphur  is  likely  to  be  changed  in  part  at  least  to  hydro- 
gen sulphide.  Moreover,  considerable  quantities  of  black 
"humus"  are  formed.  The  straw  and  other  litter  lose  their 
original  fibrous  condition  and  become  a  part  of  the  dark, 
fine  mass  of  "well-rotted  manure."  Under  anaerobic  con- 
ditions the  loss  of  carbon  dioxide,  water,  hydrogen,  and 
methane  results  in  loss  of  weight. 

192.  Molds. — Particularly  in  loose,  dry  manure,  molds 
develop  and  cause  destruction  of  both  nitrogenous  and 
non-nitrogenous  compounds.  "Fire  fanging"  is  a  result 
of  the  growth  of  molds  on  horse  manure,  resulting  in  the 
appearance  of  a  white,  powdery  coating  on  the  material. 

193.  Loss. — ^The  above  mentioned  changes  are  what  take 
place  under  special  conditions.  Considering  now  an  ordinary 
manure  pile,  such  as  is  altogether  too  common  even  now, 
it  will  be  interesting  to  note  what  happens.  Such  a  pile  is 
only  moderately  compact;  loose  on  the  outside  at  any  rate, 
and  exposed  to  the  weather.  Both  aerobic  and  anaerobic 
decomposition  take  place.  Urea  changes  rapidly  to  ammo- 
nium carbonate  and  ammonia.  Proteins  are  changing  to 
ammonia.  Ammonia  is  being  oxidized  to  free  nitrogen  as 
well  as  passing  off  into  the  air.  Carbon  dioxide  and  water 
are  being  formed  in  considerable  quantities  as  well  as  some 
hydrogen  and  methane.  The  pile  shrinks  in  volume,  losing 
weight  constantly.  Humus-like  substances  form,  many  of 
which  are  dissolved  out  by  a  solution  of  alkaline  carbonates 


248  FARM  MANURE 

formed  by  the  decomposition  of  organic  compounds  of 
potassium  and  other  alkahes,  including  some  ammonium 
carbonate.  Rain  leaches  out  these  soluble  compounds  as 
well  as  soluble  phosphates.  There  is  consequently  a  decided 
loss  of  potassium  and  phosphorus  by  leaching;  of  nitrogen 
by  volatilization  as  free  nitrogen  and  as  ammonia;  and  a 
decrease  in  amount  of  organic  matter  due  to  volatilization 
of  carbon  dioxide,  hydrogen,  and  methane,  and  to  leaching 
away  of  humus  compounds.  The  most  serious  loss,  however, 
is  that  of  nitrogen,  phosphorus,  and  potassium,  and  amounts 
under  such  conditions  to  more  than  half  of  the  original 
content  of  these  elements.  Moreover,  they  are  in  the  best 
form,  being  soluble  and  available  to  plants. 

194.  Prevention  of  Loss. — From  the  preceding  discussion, 
it  can  be  seen  that  the  greatest  loss  of  nitrogen  occurs  under 
aerobic  conditions,  while  the  loss  of  phosphorus  and  potas- 
sium and  some  of  the  nitrogen  occurs  only  when  leaching 
takes  place.  Since  it  is  possible  to  retain  a  large  part  of  the 
volatile  ammonia  by  chemical  means  as  well  as  by  producing 
anaerobic  conditions,  methods  of  preventing  loss  of  the 
fertilizing  constituents  can  be  grouped  under  two  general 
heads:   Mechanical  and  chemical. 

(a)  Mechanical. — Since  phosphorus  and  potassium  in  the 
solid  excrement,  after  being  rendered  soluble  under  either 
aerobic  or  anaerobic  conditions,  are  lost  only  by  being 
washed  out  of  the  manure  pile,  it  is  sufficient  only  to  prevent 
leaching  by  keeping  the  pile  under  cover,  or  in  a  water-tight 
receptacle;  or  piled  in  such  a  way  that  leaching  is  reduced 
to  a  minimum.  This  may  be  accomplished  by  making  the 
pile  decidedly  concave  on  top  to  hold  the  water  that  falls, 
and  building  the  sides  vertical. 

Since  a  large  part  of  the  potassium  and  nitrogen  are  in  the 
urine  and  hence  soluble,  it  is  necessary  to  take  precautions 
which  will  prevent  the  urine  from  running  off.  Litter 
accomplishes  this  purpose  if  employed  in  sufficient  quantities, 
and  particularly  if  cut  into  short  pieces — a  practice  which 
increases  the  absorptive  capacity  of  straw  two  or  three  times. 
Rock  phosphate  sprinkled  in  the  stalls  before  adding  the 
bedding  also  makes  an  excellent  absorbent  material.     This 


PREVENTION  OF  LOSS  249 

practice  not  only  reinforces  the  manure  in  phosphoric  acid 
content,  but  also  serves  to  make  the  rock  phosphate  avail- 
able to  plants  (Section  164).  Three  or  four  pounds  to  each 
animal  every  day  for  horses  and  cattle  is  a  good  amount 
to  use. 

In  addition  to  the  leaching  away  of  soluble  nitrogenous 
compounds,  a  large  part  of  the  nitrogen  is  lost  by  volatiliza- 
tion. Since  this  is  due  largely  to  aerobic  bacterial  action, 
combined  with  free  circulation  of  air  which  allows  dissociation 
of  ammonium  carbonate,  a  system  which  keeps  the  pile 
compact  and  saturated  with  water,  or  at  least  with  carbon 
dioxide,  will  answer  the  purpose.  This  may  be  accomplished 
by  compacting  either  in  piles  or  pits,  or  under  the  feet  of  the 
animals  by  the  so-called  deep-stall  system. 

If  a  pile  of  manure  is  kept  well  packed  down  and 
thoroughly  though  not  excessively  soaked  with  water  or 
surplus  urine,  air  will  not  have  access  to  the  pile  except  on 
the  surface,  and  aerobic  decomposition  will  be  reduced  to  a 
minimum.  By  this  means  nitrogen  is  not  lost  to  any  great 
extent  either  as  free  nitrogen  or  as  ammonia-. 

The  deep-stall  system  consists  in  allowing  the  manure  to 
be  compacted  by  the  feet  of  animals  in  stalls  where  the 
manure  can  accumulate  and  be  well  tramped  down,  litter 
being  liberally  used.  By  this  means  the  loss  of  nitrogen  is 
reduced  to  about  15  per  cent.,  but  the  practice  is  not  sani- 
tary and  although  used  to  some  extent  in  Europe  is  not  to  be 
recommended.  The  saving  of  nitrogen  in  manure  is  not  the 
only  thing  to  be  considered  in  caring  for  stock. 

(6)  Chemical. — In  preventing  the  loss  of  fertilizing  con- 
stituents from  manure  by  chemical  means  there  is  only 
nitrogen  to  be  considered.  Phosphorus  and  potassium 
are  easily  retained  by  preventing  leaching  and  this  is  a 
mechanical  means.  Nitrogen,  on  the  other  hand,  is  volatile 
as  ammonia  and  free  nitrogen,  hence  chemicals  which 
form  non-volatile  compounds  of  nitrogen,  or  which  prevent 
complete  decomposition,  are  employed. 

1.  Gypsum,  Land  Plaster. — By  using  gypsum,  CaS04, 
at  the  rate  of  100  pounds  to  the  ton  of  manure,  or  better 
yet  by  sprinkling  three  or  four  pounds  in  the  stall  of  each 


250  FARM  MANURE 

animal  per  day  and  then  adding  litter,  the  ammonium  car- 
bonate is  changed  to  ammonium  sulphate,  thus: 

(NHOjCOs  +  CaS04  =  (NH4)2S04  +  CaCOs. 

Ammonium  sulphate  is  non-volatile,  although  it  is  soluble, 
and  must  be  prevented  from  leaching.  The  advantage  is 
that  no  ammonia  escapes  into  the  air.  Gypsum  is  perfectly 
safe  to  use  because  it  has  no  harmful  effect  on  the  feet  of  the 
animals.  By  itself  it  has  no  fertilizing  effect  on  the  soil, 
but  after  reacting  with  ammonium  carbonate,  the  resulting 
calcium  carbonate  will  neutralize  soil  acids,  although  there 
is  but  little  present  at  any  one  time. 

2.  Acid  Phosphate. — ^This  material  may  be  used  at  the 
rate  of  50  pounds  per  ton  of  manure,  but  on  account  of  its 
harmful  effect  on  the  feet  of  animals  it  is  better  to  use  it  in 
the  gutters  or  with  manure  after  the  latter  has  been  removed 
from  the  stalls.  The  value  of  acid  phosphate  is  two-fold. 
It  holds  the  ammonia  as  ammonium  sulphate,  due  to  the 
calcium  sulphate  in  the  fertilizer.  And  furthermore,  it  rein- 
forces the  manure  with  phosphoric  acid  which  is  the  deficient 
element.  It  is  stated  that  acid  phosphate  is  the  most 
efficient  holder  of  ammonia  in  use. 

3.  Potash  Salts. — ^The  muriate  and  sulphate  of  potash, 
kainite,  or  any  of  the  salts  of  potash  used  as  fertilizers, 
except  potassium  carbonate  (see  below),  are  used  at  the 
rate  of  50  pounds  per  ton  of  manure.  These  compounds 
are  also  injurious  to  the  feet  of  animals  and  should  be  used 
like  acid  phosphate.  Ammonia  is  converted  to  ammonium 
chloride  or  sulphate  and  is  non-volatile,  although  soluble. 

4.  Sulphurous  and  Sulphuric  Acids. — ^These  acids  will 
retain  ammonia  as  the  sulphite  (later  changing  to  the 
sulphate)  and  the  sulphate,  but  they  are  not  to  be  recom- 
mended, for  their  acid  character  renders  them  harmful  to 
the  soil  if  they  are  not  completely  neutralized. 

5.  Preservatives. — To  check  bacterial  action  and  thus 
prevent  the  formation  of  ammonium  carbonate,  such  pre- 
servatives or  antiseptics  as  carbon  disulphide  and  soluble 
fluorides  have  been  employed.    Their  use,  however,  should 


METHODS  OF  USE  251 

be  discouraged,  for  they  are  not  only  expensive,  but  by 
interfering  with  the  activity  of  bacteria  in  manure  destroy 
one  of  its  most  valuable  functions,  namely,  that  of  supplying 
microorganisms  to  the  soil. 

6.  Lime  Should  Never  be  Used. — In  this  connection  it 
must  be  emphasized  that  for  the  preservation  of  nitrogen 
or  absorption  of  liquid  in  stalls,  lime  should  never  be  used. 
It  does  not  hold  the  ammonia,  but  rather  causes  its  loss  by 
releasing  it  from  any  of  its  compounds.  Ground  limestone 
is  not  so  bad  in  this  respect  as  burnt  lime.  Wood  ashes 
should  never  be  used  because  the  potassium  carbonate  will 
drive  off  ammonia  even  more  readily  than  burnt  lime. 
The  use  of  lime  in  composting,  however,  is  allowable,  but 
for  a  different  purpose  if  proper  precautions  are  taken 
(Section  195,  c). 

195.  Methods  of  Use. — There  are  only  a  few  points  to  be 
brought  out  in  a  work  of  this  kind.  A  more  complete  treat- 
ment of  the  subject  is  better  suited  to  a  discussion  of  special 
crops  and  methods  of  farming. 

(a)  Fresh  Manure. — Experiments  show  conclusively 
that  better  yields  are  secured  on  ordinary  soils  from  manure 
hauled  fresh  to  the  fields  than  from  manure  that  has  stood 
in  the  pile  for  some  time  even  under  optimum  conditions. 
This  is  principally  due  to  the  fact  that  all  the  fertilizing 
material  has  been  retained  and  that  the  maximum  effect 
of  bacteria  in  decomposing  organic  matter  and  dissolving 
mineral  plant  food  has  been  obtained.  Manure  which  has 
been  hauled  fresh  to  the  fields  can  be  spread  on  the  surface 
of  the  soil  and  allowed  to  lie  exposed  without  danger  of  loss 
of  nitrogen,  for  the  sun  will  check  bacterial  action  directly, 
and  also  by  drying  the  manure  will  thus  deprive  the  bacteria 
of  their  necessary  moisture.  Fresh  manure  can  be  applied 
on  top  of  the  snow  with  success.  No  loss  of  ammonia  will 
occur,  and  as  the  snow  melts  the  soluble  fertilizing  ingredients 
soak  into  the  soil.  This  practice,  however,  is  not  safe  on 
frozen  hillsides  where  there  is  danger  of  loss  of  these  soluble 
compounds  by  being  washed  away  over  the  frozen  soil. 

(6)  Well  Decomposed  Manure. — Sometimes,  however, 
it  is  not  economical  to  spread  manure  at  once.    It  may  cost 


252  FARM  MANURE 

more  to  haul  it  fresh  to  the  fields  than  the  increase  in  crops 
would  be  worth.  In  such  cases  the  application  of  decomposed 
manure  should  be  followed  at  once  by  plowing  or  harrowing, 
or  be  made  just  before  a  rain  which  will  wash  into  the  soil 
ammonium  carbonate  previously  formed.  In  the  fresh 
manure  ammonium  carbonate  has  not  been  produced,  so 
its  loss  need  not  be  feared. 

On  light  soils  well  decomposed  manure  has  some  advan- 
tages over  fresh  manure,  since  the  latter  would  make  the  soil 
only  more  open  and  porous  and  would  burn  out  quickly.  The 
nitrogen  of  well  decomposed  manure  is  not  so  available  as 
that  of  fresh  manure,  for  much  of  it  has  been  decomposed 
to  soluble  compounds  and  back  again  to  proteins  in  the 
bodies  of  bacteria.  The  phosphorus  and  potash,  on  the 
other  hand,  are  more  available.  On  account  of  these  facts, 
the  action  of  well  decomposed  manure  is  more  uniform  and 
under  certain  special  conditions  is  desirable. 

(c)  Composted  Manure. — ^This  is  a  practice  resorted  to 
by  vegetable  growers,  largely  to  get  the  manure  quickly  into 
a  thoroughly  decomposed  and  disintegrated  condition.  The 
objects  are  to  get  the  manure  in  a  fine  state  of  division  for 
easy  mixing  with  the  soil,  and  to  make  the  fertilizing  con- 
stituents more  uniformly  available.  As  mentioned  before, 
fresh  manure  contains  more  available  nitrogen  than  decom- 
posed manure,  and  when  used  in  large  quantities  fresh  manure 
produces  too  great  a  leaf  growth  on  roots  or  other  similar 
crops,  due  to  excess  of  nitrogen.  The  manure  is  piled  in 
alternate  layers  with  some  absorbent  like  soil.  All  sorts  of 
organic  refuse  can  be  added  and  sometimes  bones,  commercial 
fertilizers,  and  lime.  The  pile  should  be  well  covered  with 
earth  and  kept  reasonably  moist.  The  alternate  layers  and 
covering  of  soil  adsorb  ammonia  which  is  generated  freely 
under  these  conditions,  particularly  if  lime  is  present.  The 
pile  is  thoroughly  turned  over  from  time  to  time — a  practice 
which  hastens  decomposition  and  the  formation  of  nitrates. 
The  organic  matter  of  bones  in  a  compost  heap  is  so  de- 
composed that  they  can  be  easily  ground.  If  lime  is  used, 
particular  care  must  be  exercised  to  keep  plenty  of  absorbing 
material  in  the  pile,  and  to  cover  it  well. 


VALUE  OF  MANURE  253 

196.  Manure  an  Unbalanced  Fertilizer. — As  a  complete 
fertilizer  manure  is  not  well  balanced.  It  contains  0.5  per 
cent,  of  nitrogen,  0.25  per  cent,  of  phosphoric  acid,  and  0.5 
per  cent,  of  potash.  Proportionately  expressed  this  is  a 
2-1-2  fertilizer.  A  common  fertilizer  for  general  farm  crops 
is  a  1-6-4  combination  (Section  201),  and  for  garden  crops  a 
4-8-10  fertilizer  is  used.  Manure  is  very  deficient  in  phos- 
phoric acid,  and  in  order  to  obtain  enough  of  this  con- 
stituent it  is  necessary  to  apply  in  many  cases  more  manure 
than  is  economically  profitable.  While  it  is  possible  to 
maintain  the  fertility  of  a  soil  for  a  long  period  of  years,  at 
least  with  no  other  fertilizer  than  manure,  it  is  not  a  practice 
to  be  recommended.  Manure  reinforced  with  phosphoric 
acid  is  more  satisfactory  and,  better  yet,  a  judicious  use  of 
commercial  fertilizers  and  manure,  properly  distributed  in 
a  rotation  according  to  the  crops,  is  to  be  recommended. 
It  is  by  no  means  a  good  practice  to  add  such  excessive 
amounts  of  manure  as  are  used  in  some  sections  of  the  country 
on  tobacco  land  where  an  average  of  eighteen  tons  of  manure 
per  acre  have  been  applied  annually.  Under  these  con- 
ditions the  loss  of  the  fertilizing  constituents  from  the 
surface  soil  has  been  enormous. 

197.  Value  of  Manure. — The  proper  use  of  barnyard 
manure  is  something  to  be  earnestly  recommended  on  every 
farm.  No  other  single  material  will  do  so  much  for  the 
soil,  and  no  other  material  is  so  cheap  and  easily  obtained 
in  most  cases.  Manure  adds  organic  matter  to  the  soil, 
and  organic  matter,  it  will  be  remembered,  improves  the 
physical  condition  of  the  soil,  increases  the  moisture  holding 
capacity  and  the  temperature  of  soils.  Moreover,  organic 
matter  is  the  source  of  carbon  dioxide  and  organic  acids 
which  aid  in  making  mineral  compounds  soluble.  This  is 
particularly  true  of  fresh  manure  which  decomposes  easily. 
Manure  also  adds  large  numbers  of  bacteria  to  the  soil, 
and  the  benefits  to  be  derived  from  bacteria  are  too  numerous 
to  mention.  And  finally  manure  adds  nitrogen,  phosphoric 
acid,  potash,  and  even  calcium  to  the  soil.  Fig.  68  shows 
the  effect  of  manure  on  a  soil  which  does  not  respond  to 
liming,  although  somewhat  acid.  It  is  probably  the  effect 
of  the  plant  food  in  the  manure  which  is  here  most  important. 


254 


FARM  MANURE 


All  these  valuable  properties  of  manure,  moreover,  are 
lasting  in  effect.  An  application  of  manure  shows  by  in- 
creased yields  for  many  years  afterwards,  whereas  the  effect 


REFERENCES  255 

of  commercial  fertilizers  lasts  but  a  few  years  at  most  and 
usually  but  one  or  two. 

EXERCISES 

1.  Give  all  the  reasons  you  can  why  it  is  not  good  practice  to  permit  a 
manure  pile  to  remain  exposed  for  months. 

2.  Why  do  nitrates  form  in  a  composted  manure  heap  to  a  greater  extent 
than  in  an  ordinary  pile? 

3.  Should  basic  slag  be  mixed  with  manure  to  reinforce  the  phosphorus 
content?     Why? 

4.  What  causes  the  color  of  the  water  leaching  away  from  an  exposed 
manure  pile?  Explain  in  detail  how  these  coloring  substances  were  prob- 
ably formed.^ 

5.  Why  do'  you  think  the  following  statement  is  good  or  poor  advice? 
"Buy  nitrogen  in  concentrated  feeds  rather  than  in  commercial  fertilizers." 

6.  Do  you  think  that  reinforcing  manure  with  a  phosphate  is  good  farm 
practice?     If  so,  what  phosphate  would  you  use? 

7.  As  components  of  what  substances  will  N,  P  and  K  probably  occur  in 
the  solid  and  liquid  excreta? 

8.  Is  manure  a  balanced  fertilizer?  a  complete  fertilizer?  a  high-grade 
fertilizer?  a  readily  available  fertilizer?  a  fertilizer  that  will  leave  a  soil 
acid?  a  necessary  fertilizer?  a  lasting  fertilizer?  a  commercial  fertilizer? 

9.  Of  the  following  which  manure  would  you  prefer:  Produced  by  a 
fattening  animal;  an  animal  giving  milk;  a  growing  animal;  a  mature,  hard- 
working animal;  a  mature  animal  not  hard-working? 

REFERENCES 

Hall.     Fertilisers  and  Manures. 
Thorne.     Farm  Manures. 
Van  Slyke.     Fertilizers  and  Crops. 
Wheeler.     Manures  and  Fertilizers. 


CHAPTER  XIV 

SOIL  AND  FERTILIZER  ANALYSIS 

The  analysis  of  soils  and  fertilizers  is  such  an  important 
part,  both  of  scientific  and  practical  agriculture,  that  there 
is  necessary  a  brief  discussion  of  the  terms  used,  of  the  possi- 
bilities and  limitations  of  such  work,  and  of  the  immediate 
value. 

198.  How  Analytical  Results  are  Expressed. — It  is  custom- 
ary in  ordinary  analytical  work  to  express  results  in  terms 
of  the  oxide  of  the  element,  thus:  CaO,  K2O,  Fe203,  P2O5. 
This  is  not  the  form  in  which  these  elements  occur,  but 
is  a  convenient  and  conventional  means  of  expression.  In 
fertilizer  work  the  elements  usually  determined  are  nitrogen, 
phosphorus,  and  potassium,  and  reported  as  nitrogen,  N, 
phosphoric  acid,  P2O5,  and  potash,  K2O.     Phosphoric  acid 

.  is  not  the  correct  name  for  the  oxide  of  phosphorus — P2O5 — 
but  since  the  oxide  is  the  acid  oxide  there  is  some  excuse  for 
it.  Furthermore,  it  is  not  consistent  to  express  nitrogen 
as  the  element,  and  phosphorus  and  potassium  as  the  oxides. 
There  is  a  desire  on  the  part  of  some  chemists  to  express 
these  and  other  results  in  the  elemental  form.  It  is  the 
logical  way  to  do,  but  since  custom  is  so  strong,  and  since 
most  farmers  and  scientists  think  in  the  conventional  terms, 
these  inconsistent  forms  have  been  used  here. 

199.  Soil  Analysis. — The  popular  conception  of  the  pur- 
pose of  soil  analysis  is  to  ascertain  the  fertilizer  deficiencies 
of  a  soil.  That  is,  by  determining  in  some  way  the  amount 
of  nitrogen,  phosphoric  acid,  and  potash,  the  need  of  a 
soil  for  any  particular  element  can  be  predicted.  This 
idea  has  resulted,  of  course,  in  the  development  of  a  large 
number  of  methods,  and  in  the  analyses  of  a  large  number 

(256) 


SOIL  ANALYSIS  257 

of  soils,  together  with  the  publication  of  a  large  number  of 
predictions.  Some  of  these  predictions  have  proved  correct; 
some  of  them  incorrect;  and  some  of  them  have  never  been 
put  to  the  proof.  The  difficulties  in  the  way  of  determining 
accurately  fertilizer  deficiencies  of  a  soil  are  so  many  that 
an  analysis  alone  cannot  give  the  information  desired  in  a 
great  majority  of  cases.  Fertilizer  tests  in  the  field  are  the 
best  single  way  to  ascertain  the  plant  food  needs  of  a  soil 
(Fig.  69). 

The  total  amount  of  each  of  the  several  constituents  can 
be  determined  accurately,  and  the  result  is  a  complete 
inventory  of  the  plant  food  supply  in  any  given  soil,  pro- 
vided the  sampling  has  been  done  carefully.  It  is  very 
important  to  obtain  a  sample  of  soil  which  represents  as 
nearly  as  possible  the  soil  of  the  whole  field  in  question. 
This  information  in  connection  with  other  data,  such  as 
topography,  physical  condition  of  the  soil,  kind  of  seed, 
cultivation,  temperature,  rainfall,  and  appearance  of  crop, 
will  give  an  expert  a  good  idea  of  the  needs  of  a  given  soil. 

The  difl[iculty  with  this  kind  of  analysis  in  interpreting 
plant  food  deficiencies  is  that  by  no  means  all  of  any  par- 
ticular element  is  available  or  will  even  become  available 
readily.  A  soil  may  contain  a  large  amount  of  phosphoric 
acid,  but  may  have  it  in  such  unavailable  form  that  plants 
cannot  obtain  enough  for  normal  growth,  and  a  phosphate 
fertilizer  is  actually  needed.  On  the  other  hand,  another 
soil  may  contain  a  very  small  amount  of  phosphoric  acid 
and  yet  have  it  in  readily  available  form.  Of  course,  if 
a  constituent  is  present  in  ridiculously  small  amounts  a 
deficiency  in  that  constituent  may  be  suspected. 

Various  methods  have  been  developed  for  determining 
available  or  readily  available  plant  food.  Strong  hydro- 
chloric acid  has  been  used  more  largely  than  any  other 
reagent  to  extract  those  constituents  which  it  is  assumed 
will  be  most  readily  available  to  plants.  Most  of  the  soil 
analyses  published  have  been  made  by  this  method.  But 
the  results  mean  very  little  for  interpreting  fertilizer  de- 
ficiencies. There  is  no  accurate  standard  or  minimum 
amount  known,  below  which  a  fertilizer  need  is  indicated. 
17 


258 


SOIL  AND  FERTILIZER  ANALYSIS 


The  minimum  varies  with  kinds  of  soils,  kinds  of  crops, 
and  many  other  factors. 


Numerous  weak  organic  acids  and  dilute  mineral  acids  have 
been  proposed  as  solvents,  and  some  methods  seem  reasonably 


LIME  REQUIREMENT  259 

good  for  certain  special  soils,  but  there  are  no  methods 
of  general  applicability.  Pure  water,  or  water  charged  with 
carbon  dioxide,  might  seem  an  excellent  solvent,  but  against 
this  solvent  as  against  others  for  that  matter,  though  in 
lesser  measure,  the  power  of  chemical  and  physical  absorp- 
tion acts  to  prevent  the  extraction  of  plant  food  that  may 
be  readily  available  to  plants  in  the  soil.  Moreover,  in  all 
these  methods  it  is  not  the  amount  of  plan;  food  available 
at  any  one  time  which  nourishes  the  crop,  it  is  the  plant 
food  available  from  day  to  day  throughout  the  growing 
season.  It  is  the  rate  at  which  plant  food  becomes  avail- 
able that  determines  crop  growth. 

But  soil  analysis  is  of  very  great  value  to  the  soil  chemist 
in  determining  changes  which  take  place  in  the  soil  under 
certain  conditions,  and  in  comparing  one  soil  with  another, 
all  of  which  work  is  valuable  in  studying  the  effect  of 
fertilizers,  the  effect  of  changing  physical  conditions,  and 
the  effect  of  cropping.  The  knowledge  so  obtained  can  later 
be  practically  applied  to  help  the  farmer  obtain  better  and 
larger  crops. 

200.  lime  Requirement. — Since  acidity  is  a  very  prevalent 
condition  of  many  soils,  and  since  it  needs  correction  in 
most  instances,  numerous  efforts  have  been  made  to  deter- 
mine the  amount  of  acid  in  a  soil ;  or^  which  is  more  direct, 
to  determine  the  amount  of  lime  necessary  to  neutralize 
acidity  to  a  given  depth.  The  method  which  has  given  the 
best  results  is  one  devised  by  F.  P.  Veitch.  Equal  weights 
of  soil  are  treated  with  different  amounts  of  lime  water 
until  one  amount  is  found  which  leaves  the  soil  slightly 
alkaline.  Knowing  the  weight  of  soil  in  the  sample,  the 
weight  of  lime  applied,  and  the  weight  of  an  acre  of  soil  to 
the  given  depth,  the  amount  of  lime  in  pounds  per  acre 
needed  to  correct  the  acidity  can  be  calculated.  The  results 
are  only  approximate  at  best,  but  the  method  serves  to 
compare  the  relative  amounts  of  lime  needed  on  different 
soils,  or  on  a  soil  under  different  treatments.  It  is  not 
sufficiently  accurate  to  tell  a  farmer  just  how  much  lime  to 
put  on  a  given  field,  although  it  may  be  a  guide  to  the  expert 
in  determining  the  amount. 


260  SOIL  AND  FERTILIZER  ANALYSIS 

There  are  two  tests  for  telling  whether  or  not  a  soil  is 
acid,  but  not  how  acid.  One  is  by  the  use  of  blue  litmus 
paper.  A  strip  of  blue  litmus  paper  is  placed  in  the  bottom 
of  a  beaker  or  tumbler  and  on  top  of  this  a  piece  of  filter 
paper  or  clean  white  blotter  cut  to  fit  the  bottom  of  the 
vessel.  The  soil  to  be  tested  is  added  until  the  dish  is  half 
full,  and  is  then  soaked  with  pure  water.  Another  beaker 
or  tumbler  is  prepared  the  same  way  but  no  soil  added. 
This  is  to  test  the  paper  and  water  for  acids.  If  the  litmus 
paper  in  the  beaker  containing  the  soil  has  turned  red 
after  standing  an  hour,  the  soil  is  acid,  the  degree  of  acidity 
depending  on  the  amount  and  rapidity  of  coloration.  At  the 
same  time  the  litmus  paper  in  the  beaker  containing  no 
soil  must  remain  blue.  If  it  turns  red  the  paper  or  water 
contains  acid  and  a  fresh  test  must  be  made  using  different 
paper  and  water. 

Another  test  is  to  add  two  or  three  ounces  of  soil  to  a 
beaker  or  tumbler  full  of  dilute  ammonium  hydroxide, 
made  by  mixing  one  part  of  strong  ammonia  with  five  parts 
of  pure  water.  After  standing  some  time  an  acid  soil  will 
yield  a  brown  or  black  color  to  the  liquid,  due  to  the  solubility 
of  the  humus  acids  in  ammonium  hydroxide  (Section  119). 
A  neutral  or  alkaline  soil  will  not  yield  a  color  to  the  liquid 
beyond  that  which  will  be  imparted  to  it  by  the  fine  soil 
particles  held  in  suspension. 

201.  Fertilizer  Analysis. — ^The  total  amount  of  plant  food 
in  fertilizers  can  be  determined  accurately  and,  with  the 
possible  exception  of  nitrogen,  the  available  material  can 
also  be  determined.  In  buying  a  fertilizer  a  farmer  ordina- 
rily wants  something  which  is  quickly  available  to  his  crops. 
State  laws  now  require  fertilizer  manufacturers  to  give  the 
analysis  with  every  fertilizer.  This  analysis  usually  consists 
of  total  nitrogen;  water  soluble,  citrate  soluble,  insoluble, 
and  total  phosphoric  acid;  and  water  soluble  potash. 

There  are  methods  which  attempt  to  determine  available 
nitrogen,  but  except  for  the  determination  of  nitrates  and 
ammonia  which  are  satisfactory,  there  are  no  really  good 
methods.  As  a  matter  of  fact,  however,  a  determination 
of  total  nitrogen  is  usually  suflBcient.     The  use  of  certain 


FERTILIZER  ANALYSIS  261 

materials,  such  as  hair,  wool  waste,  and  leather  is  not  per- 
mitted by  some  states  in  making  complete  fertilizers  unless 
they  are  treated  with  sulphuric  acid  as  in  the  manufacture 
of  "base  goods."  Their  presence  in  the  raw  state  can  be 
detected  with  a  microscope,  and  the  farmer  is  thus  protected 
against  their  use  in  this  condition. 

Water  soluble  phosphoric  acid  is  monocalcium  phosphate, 
CaH4(P04)2,  citrate  soluble  phosphoric  acid  is  the  dicalcium 
phosphate,  Ca2H2(P04)2.  It  is  also  called  "  reverted  "phosphate 
(Section  165,  a).  The  name  "citrate  soluble"  comes  from 
the  fact  that  it  is  soluble  in  a  neutral  solution  of  ammonium 
citrate.  Both  water  soluble  and  citrate  soluble  phosphoric 
acid  are  available  to  plants,  so  that  analyses  sometimes 
give  only  the  available  phosphoric  acid  which  includes 
both  forms.  Insoluble  phosphoric  acid  is  tricalcium  phos- 
phate,  Ca3(P04)2. 

Water  soluble  potash  is  a  simple  determination,  and 
of  course  is  that  potash  which  is  readily  available  to 
plants.  The  guaranteed  analysis  does  not  state  whether  the 
potash  is  in  the  chloride  or  sulphate  form,  or  whether  these 
acid  radicles  are  present.  This  is  sometimes  important 
(Sections  168  and  169),  and  if  so  it  would  be  necessary  to 
have  the  fertilizer  analyzed  further,  or  to  buy  known 
materials. 

In  discussing  fertilizers,  and  sometimes  even  in  naming 
them,  it  is  customary  to  use  the  percentage  figures  only, 
in  the  order  of  nitrogen,  phosphoric  acid,  and  potash.  Thus, 
a  1-6-4  fertilizer  is  one  which  contains  1  per  cent,  nitrogen, 
6  per  cent,  phosphoric  acid,  and  4  per  cent,  potash. 

In  expressing  the  results  of  analyses  it  is  sometimes  custom- 
ary to  add:  "Nitrogen  equal  to  ammonia."  This  gives  a 
little  higher  figure  and  makes  the  fertilizer  look  richer  than 
it  really  is,  unless  the  purchaser  is  in  the  habit  of  thinking  of 
nitrogen  in  terms  of  ammonia,  the  way  the  fertilizer  manu- 
facturers do.  They  buy  all  nitrogenous  materials  on  the 
ammonia  basis. 

In  the  same  way  phosphoric  acid  is  sometimes  referred  to  as 
"bone  phosphate  of  lime."  Phosphoric  acid  is  P2O5,  bone 
phosphate  is  Ca3(P04)2.    Hence  the  percentage  is  more  than 


262  SOIL  AND  FERTILIZER  ANALYSIS 

doubled  by  expressing  the  amount  of  phosphorus  in  the 
latter  way. 

Potash  is  sometimes  called  "equivalent  to  sulphate." 
This  also  apparently  increases  the  amount,  almost  doubling 
the  figures. 

For  example,  a  fertilizer  containing  1  per  cent,  nitrogen, 
6  per  cent,  phosphoric  acid,  and  4  per  cent,  potash  would 
be  expressed  on  the  higher  basis  as  1.21  per  cent,  ammonia, 
13.08  per  cent,  bone  phosphate  of  lime,  and  7.40  per  cent, 
potassium  sulphate,  and  yet  it  might  contain  no  ammonia, 
no  bone  phosphate,  and  no  sulphate  of  potash. 

In  interpreting  a  fertilizer  analysis  the  farmer  need  pay 
attention  only  to  the  nitrogen,  phosphoric  acid,  and  potash, 
and  not  be  led  astray  by  the  more  attractive  higher  figures. 
It  is  only  just  to  say,  however,  that  most  of  the  fertilizers 
now  offered  for  sale  by  reputable  concerns  are  honest  goods 
with  the  guaranteed  analysis  well  stated. 

EXERCISES 

1.  How  would  you  determine  the  fertilizer  deficiencies  of  your  farm? 

2.  State  in  detail  just  why  a  good  soil  should  contain  nitrogen,  phosphorus, 
potassium,  calcium,  humus  and  bacteria. 

3.  How  test  for  the  following:  Dextrose,  starch,  protein,  fat,  a  volatile 
oil,  cellulose,  humus,  soil  acidity,  an  enzyme,  a  soluble  phosphate,  a  nitrate, 
an  ammonium  compound,  a  soluble  potassium  compound,  organic  matter 
and  limestone? 

4.  Given  750  pounds  of  acid  phosphate  containing  16  per  cent,  available 
P2C6,  167  pounds  of  muriate  of  potash  containing  48  per  cent,  available 
K2O,  607  pounds  of  sodium  nitrate  containing  16  per  cent,  available  ammo- 
nia and  enough  filler  to  make  a  ton  of  fertilizer,  how  much  filler  is  used  and 
what  is  the  formula  of  the  fertilizer? 

5.  How  many  pounds  of  nitrate  of  soda  containing  15  per  cent.  N,  and 
phosphate  containing  7  per  cent.  P,  and  muriate  of  potash  containing  42 
per  cent.  K  must  be  used  to  make  a  ton  of  a  fertilizer  selling  as  3.5-4-6.3? 
How  many  pounds  of  filler  must  be  used  to  make  this  mixture  equal  to  a 
ton  in  weight? 

6.  About  how  many  pounds  of  a  complete  fertilizer  that  sells  as  a  4-8-4 
goods  is  it  necessary  to  add  in  order  to  return  to  the  soil  the  plant  food 
removed  by  an  acre  of  corn?     Would  you  recommend  any  other  formula? 

7.  Answer  Exercise  6  for  an  acre  of  potatoes;  an  acre  of  apples. 

8.  How  much  nitrogen,  potassium  and  phosphorus  is  contained  in  a  ton 
of  a  4-8-10  fertiUzer? 

9.  Just  why  are  the  following  used  in  the  litmus  paper  test  for  soil  acidity: 
Two  beakers,  filter  paper,  water  that  is  pure? 

10.  How  is  a  sample  of  soil  taken  for  a  test  by  the  Veitch  method? 


REFERENCES  263 

11.  Which  fertilizer  would  you  buy,  and  why:  One  whose  analysis  is 
2  per  cent.  N,  6  per  cent.  PjOi  and  4  per  cent.  KjO  or  one  that  is  marked 
2.18  per  cent.  NH»,  13  per  cent,  bone  phosphate  of  lime  and  6  per  cent, 
muriate  of  potash? 

REFERENCES 

Hilgard.     Soils. 

Van  Slyke.     Fertilizers  and  Crops. 


CHAPTER  XV 
INSECTICIDES  AND  FUNGICIDES 

The  treatment  of  plants  to  destroy  insect  pests  and 
fungous  diseases  is  now  so  important  a  factor  in  the  growth 
of  crops  that  a  short  description  of  the  compounds  and 
mixtures  employed  will  be  of  value.  No  attempt  will  be 
made  to  describe  the  various  insects  and  fungi  or  to  give 
the  proper  treatment  for  each.  All  such  details  including 
methods  of  application  and  proper  dilution  of  spray  material 
should  properly  be  taken  up  in  connection  with  the  pro- 
pagation and  growing  of  various  plants.  The  present  dis- 
cussion will  be  limited  to  the  chemistry  of  the  more  common 
spray  materials,  noting  first  the  chief  characteristics  of  the 
pests  to  be  destroyed.  Figs.  70,  71,  and  72  illustrate  the 
method  and  results  of  spraying. 

202.  Insects. — ^The  insects  which  destroy  crops  are  of 
two  kinds:  First,  those  which  have  biting  mouth  parts  for 
chewing  the  plant  tissues,  such  as  grasshoppers,  caterpillars, 
and  cucumber  beetles.  Second,  those  which  have  a  beak 
or  apparatus  for  penetrating  the  skin  of  plant  organs  and 
sucking  up  the  juices.  They  do  not  chew  and  swallow  any 
of  the  tissue  proper.  The  woolly  aphis  and  San  Jose  scale 
are  examples  of  these  insects. 

For  insects  which  eat  plant  tissue,  it  is  usually  sufficient 
to  sprinkle  the  surface  of  the  leaves  with  a  poison.  This 
kills  the  insects  when  the  poison  is  taken  internally.  The 
insects  which  do  not  eat  tissue  but  suck  out  the  plant  juices 
are  not  injured  by  this  treatment.  They  penetrate  the 
skin  for  their  nourishment  and  do  not  eat  the  poison  on  the 
surface.  Spray  materials  which  kill  by  contact  are  efficacious. 
They  act  by  destroying  the  skin  of  the  insects  or  by  clogging 
up  their  breathing  pores,  or  by  merely  repelling  them. 
(264) 


FUNGI 


265 


203.  Fungi. — Fungi  are  plants  which  have  no  chlorophyl 
and  are  consequently  dependent  on  host  plants  for  all  their 
food.  They  are  propagated  by  spores  which  are  produced 
in  great  numbers  and  can  be  easily  disseminated.  When 
the  spores  germinate  on  some  suitable  host,  a  little  tube  is 
put  forth,  from  which  develops  the  mycelium.  Some  fungi 
grow  mostly  under  the  surface,  the  spore  tube  etitering  by 


Fig.  70. 


-Spraying  an  orchard.     Department  of  Experimental  Pomology, 
Pennsylvania  Station. 


the  stomata  or  other  openings  in  the  leaf  or  stem.  These  are 
fungi  like  the  brown  rot  and  grain  smuts.  Other  fungi  grow 
on  the  surface,  like  the  powdery  mildew.  Internal  fungi 
cannot  be  killed  after  they  have  gained  entrance  to  the 
host,  but  must  be  caught  before  the  spore  germinates,  by 
covering  the  plant  with  a  poison  which  kills  the  spore  or 
germ  tube.  External  fungi  can  be  killed  at  any  time  because 
they  are  always  exposed. 


266 


INSECTICIDES  AND  FUNGICIDES 


Fig.  71. — Unsprayed  fruit.    Department  of  Experimental  Pomology, 
Pennsylvania  Station. 


^^■W^^                  «  v..                                                                           .               W 

■^4^^^ 

i^  ^^tfe'        r  ; 

^r                                              ^..^^^^^^^^^^^^^^^^^tt^^i^^^^^Hti^ 

t,^ 

Fig.  72. — Sprayed  fruit.    Department  of  Experimental  Pomology, 
Pennsylvania  Station. 


INTERNAL  INSECTICIDES  267 

204.  Insecticides. — These  spray  materials  may  be  divided 
into  two  classes,  internal,  and  external  or  contact  insecti- 
cides. 

I.  INTERNAL  INSECTICIDES 

(a)  Hellebore  is  a  powder  made  by  grinding  the  dried 
roots  of  the  American  hellebore  (veratrum  viride)  or  of 
the  white  or  European  hellebore  (veratrum  album).  The 
active  constituents  are  certain  alkaloids,  said  to  be  some  six 
in  number. 

(6)  Lead  Arsenate  is  made  by  mixing  sodium  arsenate, 
Na2HAs04,  with  lead  acetate,  Pb(C2H302)2,  or  lead  nitrate, 
Pb(N03)2.  The  precipitate,  depending  on  conditions  of 
temperature,  concentration,  and  methods  of  mixing,  consists 
of  neutral  or  triplumbic  arsenate,  Pb3(As04)2,  and  acid  lead 
arsenate,  PbHAs04,  in  varying  proportions.  It  comes  on  the 
market  as  a  paste  or  powder  which  forms  a  suspension  on 
mixing  with  water  in  the  proper  proportions  for  spraying. 
When  eaten  by  insects  the  arsenic  in  the  compound  is  fatal. 

Injury  sometimes  results  to  the  leaves  from  the  use  of 
lead  arsenate.  Since  insoluble  compounds  do  not  harm  foliage 
it  is  certain  that  enough  arsenic  from  lead  arsenate  goes  into 
solution  to  penetrate  the  leaves  and  kill  the  tissues.  Con- 
sequently the  amount  of  water  soluble  arsenic  in  commercial 
preparations  of  lead  arsenate  is  limited  by  the  national 
Insecticide  Act  of  1910  to  0.75  per  cent,  of  water  soluble 
As205.^  But  injury  has  resulted  from  the  use  of  lead  arsenate 
that  came  well  within  the  law,  and  as  a  result  of  investiga- 
tion the  following  facts  have  been  discovered:  Triplumbic 
arsenate  or  the  neutral  lead  arsenate  is  insoluble  in  pure 
water  or  water  containing  chlorides,  sulphates,  or  carbon- 
ates, and  causes  no  harm  to  foliage.  The  acid  arsenate,  on 
the  other  hand,  is  slightly  soluble  in  pure  water  and  much 
more  so  in  water  containing  the  above  named  substances 
in  solution.     Injury  results  when  hard  water,  or  "alkali" 

*  Determined  by  soaking  1  gram  of  lead  arsenate  in  1000  c.c.  of  carbon 
dioxide-free  water  for  ten  days,  shaking  eight  times  a  day,  and  analyzing 
the  filtrate.  Water  soluble  A820»  in  Paris,  green  is  determined  in  the  same 
way. 


268  INSECTICIDES  AND  FUNGICIDES 

water,  is  used  in  the  preparation  of  the  spray  from  acid 
arsenate,  and  when,  furthermore,  heavy  dews  or  fogs  keep 
the  foliage  soaked  with  moisture  part  of  the  time,  and  so 
dissolve  enough  arsenic  to  injure  plant  tissue.  Rain  would 
wash  off  the  dissolved  arsenic  and  cause  no  harm.  It  is 
possible  to  purchase  lead  arsenate  at  present  which  is  guaran- 
teed to  be  the  neutral  arsenate. 

(c)  Paris  Green,  Schweinfurth  Green,  is  made  by 
boiling  arsenous  oxide,  AS2O3,  with  basic  copper  acetate, 
Cu(C2H302)2-CuO.  The  brilliant  green  precipitate  is  used 
as  a  suspension  in  spraying.  Its  chemical  name  is  copper 
aceto-metarsenite,  [Cu(As02)2]3.Cu(C2H302)2-  The  arsenic 
content  is  the  active  poison  for  insects. 

Leaf  burning  is  very  apt  to  result  from  the  use  of  Paris 
green,  due  to  water  soluble  arsenic.  The  national  Insecticide 
Act  of  1910  prohibits  the  sale  of  Paris  green  containing 
more  than  3.5  per  cent,  water  soluble  As203.^  In  addition 
to  this,  however,  the  action  of  water  and  carbon  dioxide 
will  dissolve  arsenic  according  to  the  following  equation : 

[CU(AS02)2]3.CU(C2H302)2+  IOH2O+  CO2  = 

6H3ASO3  +  CuC08.Cu(OH)2  +  Cu(C2H302)2.CuO. 

This  danger  is  so  great  that  it  is  usually  customary  to  mix 
Paris  green  with  lime  or  Bordeaux,  the  latter  containing 
an  excess  of  lime.  The  free  arsenic  is  neutralized  by  the 
lime,  thus: 

2H3ASO3  +  3Ca(OH)2  =  Ca3(As03)2  +  6H2O. 

Sometimes  Paris  green  is  adulterated  with  worthless 
articles  like  gypsum.  It  is  easy  to  test  for  such  adultera- 
tion by  treating  the  material  with  strong  ammonia.  Paris 
green  dissolves  according  to  the  following  equation: 

[Cu(As02)2]3.Cu(C2H302)2+  36NH4OH  = 
4[Cu.(NH8)4.(OH)2]  +  6(NH4)3As03  +  2NH4C2H»02  +  22H20. 

1  See  footnote,  page  267. 


EXTERNAL  INSECTICIDES  269 

The  soluble  copper  compound  called  cuprammonium  hydrox- 
ide is  written  graphically, 

/NHi— NH.— OH 
Cu< 

\NHi— NHt— OH 

and  is  the  same  thing  as  Schweitzer's  reagent  used  for 
dissolving  cellulose  (Section  9).  The  gypsum  is  left  as  an 
insoluble  residue.  So  far  as  adulterations  go,  however,  the 
Insecticide  Act  of  1910  protects  the  farmer  by  limiting  the 
minimum  amount  of  arsenous  oxide  to  50  per  cent. 


n.  EXTERNAL  INSECTICmES 

(a)  Hydrocyanic  Acid  Gas  is  a  very  violent  poison  to 
man  as  well  as  to  insects.  The  acid  at  ordinary  tempera- 
tures is  a  mobile,  volatile  liquid,  with  an  odor  of  bitter 
almonds  and  a  boiling  point  of  26.5°  C.  It  kills  insects  by 
entering  their  breathing  apparatus  and  putting  a  stop  to 
their  vital  functions.  As  used  for  fumigation  it  is  prepared 
by  treating  sulphuric  acid  with  potassium  cyanide.  The 
reaction  is: 

KCN+  H»SO«  =  KHSO«+  HCN. 

Potassium  sulphate,  K2SO4,  is  not  formed  with  the  excess 
of  sulphuric  acid  necessary  to  get  the  maximum  evolution 
of  gas.  It  is  necessary  to  use  enough  water  to  hold  the  acid 
potassium  sulphate  in  solution  after  the  reaction,  especially 
in  the  generators  used  for  the  purpose  of  producing  the  gas 
on  a  large  scale.  The  best  proportion  of  cyanide,  acid,  and 
water  is  a  1-1-3  formula,  or  1  part  potassium  cyanide  to  1 
part  of  concentrated  sulphuric  acid  (commercial  concen- 
trated acid  is  about  93  per  cent,  pure)  and  3  parts  of  water. 
The  use  of  much  stronger  sulphuric  acid  results  in  the 
decomposition  of  hydrocyanic  acid  and  the  formation  of 
ammonia  and  formic  acid  or  carbon  monoxide  depending  on 
the  strength  of  the  sulphuric  acid.  The  ammonia  forms 
ammonium  sulphate  with  the  acid. 


270  INSECTICIDES  AND  FUNGICIDES 

The  use  of  sodium  cyanide  is  preferable  in  some  ways,  since 
more  hydrocyanic  acid  gas  can  be  Hberated  from  a  pound 
of  sodium  cyanide  than  from  a  pound  of  potassium  cyanide, 
because  of  the  lower  atomic  weight  of  sodium.  100  parts  of 
sodium  cyanide  is  equal  to  132  parts  of  potassium  cyanide 
in  theoretical  effectiveness.  The  reaction  is  similar,  but 
the  sodium  acid  sulphate  is  more  soluble  than  the  corre- 
sponding potassium  salt  and  a  3-4-6  formula  is  recommended. 

The  trouble  which  is  sometimes  experienced  in  obtaining 
good  results  from  the  use  of  potassium  cyanide  is  due  in 
part  to  the  presence  of  sodium  chloride.  Sulphuric  acid 
sets  free  hydrochloric  acid,  and  the  latter  forms  ammonia, 
later  ammonium  chloride,  and  formic  acid.  This  reaction 
of  course  reduces  the  yield  of  hydrocyanic  acid  gas.  It  is 
not  sufficient  that  the  potassium  cyanide  have  a  guarantee 
of  98  per  cent,  pure,  for  a  mixture  of  potassium  and  sodium 
cyanides  would  show  98  per  cent,  expressed  as  potassium 
cyanide  and  yet  have  considerably  more  than  2  per  cent,  of 
sodium  chloride  present.  If  possible  the  amount  of  sodium 
chloride  present  should  be  known,  and  it  is  recommended 
not  to  have  more  than  1  per  cent. 

Since  the  use  of  hydrocyanic  acid  gas  is  attended  with 
great  danger  to  the  operator,  extreme  pains  should  be  taken 
by  him  not  to  inhale  the  gas  himself,  or  generate  it  where 
others  may  run  any  risk.  It  is  altogether  too  dangerous  to 
handle  with  impunity,  and  too  much  carelessness  is  displayed 
in  its  use. 

(6)  Kerosene  Emulsion. — Kerosene,  or  coal  oil,  as  it  is 
sometimes  called,  is  an  excellent  contact  insecticide,  killing 
by  entering  the  pores  of  the  insect.  Used  in  the  pure  state, 
however,  it  is  apt  to  harm  vegetation,  and  is  not  much 
employed.  It  is  one  of  the  fractional  distillation  products 
from  crude  petroleum  and  consists  of  a  mixture  of  paraffine 
or  methane  hydrocarbons  whose  boiling  points  lie  between 
150°  and  300°  C.  Kerosene  is  insoluble  in  water  and  hence 
cannot  easily  be  diluted,  although  attempts  have  been  made 
to  agitate  the  two  together  so  as  to  obtain  a  mechanical 
mixture  suitable  for  application  to  trees,  but  the  mixture 
separates  too  rapidly  to  be  satisfactory.     By  thoroughly 


EXTERNAL  INSECTICIDES  271 

agitating  kerosene  with  a  solution  of  hard  or  soft  soap,  there 
is  obtained  an  emulsion  which,  when  properly  made,  retains 
its  permanency  for  at  least  several  days. 

An  emulsion  is  a  mechanical  mixture  of  two  liquids  in- 
soluble in  each  other.  One  is  usually  an  oil,  the  particles  of 
which  are  very  finely  divided  and  are  held  in  suspension 
in  the  other  which  is  of  a  gelatinous  or  viscous  nature.  The 
permanency  of  suspension  is  brought  about  partly  because 
the  particles  are  very  small  and  the  friction  in  moving 
through  the  suspending  liquid  is  sufficient  to  prevent  their 
accumulating  rapidly;  and  partly  because  the  suspending 
liquid  exerts  some  physical  if  not  chemical  attraction  for 
the  particles,  thus  helping  to  prevent  their  uniting  with  one 
another.  Moreover,  each  fine  particle  of  oil  is  surrounded 
by  a  coating  of  the  gelatinous  or  viscous  suspending  liquid 
and  can  not  easily  touch  another  particle  to  coalesce  with  it. 
The  finer  the  particles  of  oil,  the  more  surface  exposed,  and 
hence  the  greater  the  attraction  of  the  suspending  liquid  for 
the  oil,  and  the  more  friction  in  moving.  Kerosene  and  soap 
solution  are  liquids  of  the  character  just  described. 

(c)  Lime-Sulphur  Boiled  is  made  by  boiling  together 
for  about  an  hour,  or  until  the  sulphur  is  dissolved,  50 
pounds  of  pure  lime  and  100  pounds  of  finely  ground 
sulphur  in  50  to  55  gallons  of  water.  The  lime  is  slaked 
before  actual  boiling  is  begun.  When  properly  made  there 
are  formed  the  tetra-  and  pentasulphides  of  calcium  and 
calcium  thiosulphate.  The  exact  reaction  is  not  known, 
but  the  following  is  given  as  a  possibility: 

3Ca(OH)2  +  llS  =CaS20>+CaS4+CaS6+3H«0. 

This  reaction  corresponds  fairly  well  to  the  proportions 
of  lime  to  sulphur  recommended,  and  to  the  amount  of 
sulphur  in  solution  as  thiosulphate  and  sulphides  found 
by  analysis. 

Lime  containing  magnesia  should  not  be  used,  for  mag- 
nesium forms  no  compounds  with  the  sulphur  and  only 
serves  to  increase  the  amount  of  sediment.  Long  boiling 
changes  the  thiosulphate  to  insoluble  sulphite  (Reaction  1); 


272  INSECTICIDES  AND  FUNGICIDES 

oxidizes  the  sulphite  to  insoluble  sulphate  (Reaction  2); 
and  the  sulphide  to  thiosulphate  (Reaction  3),  with  a 
separation  of  sulphur  in  each  case  except  the  second.  Ex- 
posure to  the  air  causes  the  oxidation  changes  to  take  place. 
The  reactions  are  as  follows: 

1.  CaSjOs=CaS08+S 

2.  CaS03+0=CaS04 

3.  CaS«+30=CaS208+2S 

The  active  constituents  as  a  contact  insecticide  are  the 
polysulphides  which  are  caustic  in  nature,  destroying  the 
skin  of  insects.  The  more  sulphides  in  solution,  the  more 
effective  the  spray;  and  much  variation  from  the  formula 
given,  or  boiling  too  long,  or  use  of  impure  materials,  all 
lessen  the  amount  of  sulphides  formed. 

Lime-sulphur  is  also  a  fungicide  and  in  addition  to  the 
sulphides,  the  thiosulphate  has  value  for  this  purpose. 
When  sprayed  on  the  trees  and  exposed  to  the  air,  the 
thiosulphate  and  sulphides  oxidize  as  indicated  in  Reactions 
1  and  3.  The  insoluble  sulphite  and  sulphur  which  are 
formed  are  also  useful  as  fungicides.  The  carbon  dioxide 
of  the  air  also  breaks  up  lime-sulphur  as  follows: 

CaS4+COj+HjO  =CaC08+H2S+3S 

Injury  to  foliage  from  the  use  of  this  spray  is  due  to  the 
caustic  effect  of  the  polysulphides,  and  occurs  for  the  most 
part  when  the  sulphides  occur  in  too  great  concentration 
or  when  they  penetrate  the  surface  of  the  leaf  through  cracks 
or  stomata.  Applied  too  thickly  the  drops  coalesce  and  run 
to  the  edge  where  by  evaporation  the  solution  becomes  suffi- 
ciently concentrated  to  destroy  leaf  tissue.  Injury,  however, 
takes  place  only  during  the  early  part  of  the  application, 
for  the  longer  the  spray  stays  on  the  leaves  the  more  the 
sulphides  are  broken  up  as  described  above. 

Although  there  is  some  evidence  that  lime-sulphur  is  an 
internal  as  well  as  an  external  insecticide,  its  action  in  this 
respect  is  not  sufficiently  pronounced  for  general  use,  and 
it  is  advantageous  if  some  internal  insecticide  can  be  mixed 
with  the  lime  sulphur,  so  that  one  spraying,  or  series  of 


EXTERNAL  INSECTICIDES  273 

sprayings,  may  be  useful  for  biting  insects,  sucking  insects, 
and  fungi,  Paris  green  is  not  satisfactory  because  it  is 
decomposed,  freeing  arsenous  acid  and  injuring  foliage. 
Lead  arsenate  is  the  best  material  to  use,  and  this  in  the 
triplumbic  form.  The  acid  arsenate  is  not  satisfactory,  on 
account  of  the  formation  of  a  soluble  arsenic  compound, 
possibly  arsenic  acid.  The  reactions  which  take  place  when 
lead  arsenate  is  mixed  with  lime-sulphur  are  complex  and 
not  well  known.  Apparently,  among  other  compounds,  lead 
sulphide  is  formed,  and  there  is  an  increase  in  the  amount 
of  thiosulphate  and  sulphite. 

Some  commercial  preparations  of  lime-sulphur,  particularly 
the  dry  powders  which  are  to  be  dissolved  in  water,  consist 
largely  of  sulphides  of  sodium  or  potassium.  These  com- 
pounds are  fungicides  not  contact  insecticides,  and,  further- 
more, their  use  with  arsenicals  causes  foliage  injury  due  to 
a  greater  solution  of  arsenic  acid. 

(d)  MisciBLE  OR  Soluble  Oils. — Not  only  kerosene,  but 
crude  petroleum  also  has  valuable  insecticidal  properties. 
Its  use,  however,  like  the  use  of  kerosene  in  the  pure  state, 
is  not  possible  on  account  of  its  injury  to  trees.  To  facilitate 
the  proper  dilution  of  these  oils  which  can  be  so  valuable, 
the  so-called  miscible  or  soluble  oils  have  been  prepared. 

For  this  purpose  there  is  made  first  an  "emulsifier"  which 
is  essentially  a  soft,  carbolated  soap,  made  commonly  by 
boiling  10  gallons  of  menhaden  oil,  8  gallons  of  carbolic  acid, 
and  15  pounds  of  caustic  potash,  then  mixing  with  it  2 
gallons  of  kerosene  and  2  gallons  of  water.  This  emulsifier 
is  then  mixed  with  varying  amounts  of  other  oils  such  as 
crude  petroleum,  paraffine  oil,  rosin  oil  (Section  29,  h), 
and  more  kerosene.  This  final  solution  is  the  miscible  oil 
and  when  mixed  slowly  with  water  according  to  the  spray 
requirements  forms  a  milky  emulsion  that  is  reasonably 
permanent  if  care  is  used  in  making  and  mixing. 

(e)  Pyrethrum,  Persian  Insect  Powder,  Buhach,  is 
made  by  grinding  the  dried  flowers  of  various  species  of  the 
pyrethrum  plant.  The  active  constituent  is  a  volatile  oil  of 
strong  characteristic  odor  which  can  be  extracted  by  ether.  It 
varies  in  amount  from  5  to  10  per  cent.    It  is  green  to  brown 

18 


274  INSECTICIDES  AND  FUNGICIDES 

in  color  and  on  exposure  to  the  air  oxidizes  to  an  inactive 
resin.  This  explains  the  necessity  of  keeping  the  powder 
in  air  tight  containers,  otherwise  it  loses  its  efficacy.  Pyre- 
thrum  is  not  poisonous  to  man. 

(/)  Tobacco. — ^An  old  remedy  for  certain  delicate  insects 
like  plant  lice  has  been  a  simple  decoction  of  tobacco  leaves 
or  waste.  The  water  extracts  the  alkaloid  nicotine  (Section 
37,  e)  which  is  active  in  destroying  insects.  Besides  a  liquid 
extract,  powdered  tobacco  and  the  smoke  of  tobacco  are 
efficacious  in  some  instances.  The  latter  contains  some 
nicotine,  but  in  addition  decomposition  products  which 
have  some  toxic  effect.  Commercial  preparations  are  on 
the  market,  many  of  them  containing  nicotine  sulphate  as 
the  active  constituent.  It  will  be  remembered  (Section  .36) 
that  alkaloids  are  basic  in  character  and  will  unite  to  form 
salts  with  mineral  acids. 

(g)  Whale  Oil  Soap. — Only  the  name  is  left  of  what  used 
to  be  the  soap  made  from  whale  oil.  Now  almost  any  kind 
of  cheap  fish  oil  is  used  and  saponified  with  potassium  or 
sodium  hydroxide.  The  potash  soap  is  soft;  it  is  more 
readily  soluble  in  hot  water,  and  the  solution  does  not 
harden  when  cold.  It  is  also  more  penetrating  and  effective. 
One  pound  of  soap  in  4  to  10  gallons  of  water  are  the  pro- 
portions ordinarily  used.  The  sticky  soap  solution  clogs 
up  the  pores  of  the  insects  and  causes  death. 

205.  Fungicides. — (a)  x\mmonl\cal  Copper  Carbonate 
is  a  solution  of  basic  copper  carbonate,  CuC03.Cu(OH)2,  or 


/OH 
Cu<' 

)>c=o 

.0 

^OH 

dissolved 

in  ammonia 

to  form  cuprammonium 

carbonate, 

Cu(NH,)4C03.H20, 

NHr— NHa— OH 

/ 

Cu 

OH 

\ 

] 

/ 
STHi— NH»— 0— C=0 

FUNGICIDES  276 

Dilute  ammonia  dissolves  more  copper  carbonate  than  strong 
ammonia,  so  that  it  is  better  to  use  dilute  ammonia  in 
dissolving  the  copper  carbonate,  rather  than  to  use  strong 
ammonia  for  solution  and  to  dilute  it  afterward.  Excess 
of  ammonia  harms  vegetation,  hence  care  must  be  used 
in  dissolving  the  copper  carbonate.  The  soluble  copper  is 
the  active  fungicide  and  in  this  form  is  not  so  dangerous  to 
foliage  as  is  copper  sulphate  which  is  sometimes  used  in 
dilute  solution. 

When  diluted  considerably,  basic  copper  carbonate  is 
apt  to  precipitate  out  and  in  such  cases  an  agitator  can  be 
used  in  the  spray,  although  if  the  spray  is  used  immediately 
after  dilution,  it  can  be  brought  on  the  plants  before  pre- 
cipitation begins. 

(6)  Bordeaux  Mixture  is  usually  made  by  mixing 
equal  parts  of  copper  sulphate  and  burnt  lime,  the  former 
previously  dissolved  in  water,  and  the  latter  slaked 
and  mixed  with  an  equal  quantity  of  water.  The  pro- 
portions vary  with  the  different  uses  of  the  fungicide. 
Formerly  the  reaction  was  thought  to  be  a  simple  one  by 
which  copper  hydroxide  and  calcium  sulphate  were  formed, 
but  this  is  impossible.  The  mixture  would  gradually  turn 
black  if  copper  hydroxide  were  formed.  Copper  hydroxide, 
Cu(0H)2,  blue,  changes  to  Cu(OH)2.(CuO)2,  and  finally 
CuO,  black.  The  color  is,  however,  very  permanent  and 
there  is  some  evidence  to  show  that  the  compound  formed 
is  a  double  basic  sulphate  of  copper  and  calcium  to  which 
has  been  given  the  formula,  (CuO)io.S03.  (CaO)4.S03.  Graphi- 
cally it  can  be  written  as  follows: 


o— Ca 

/ 

s 

O— Cu         Cu        Cu         Cu         Cu        Cu         Cu 

\/  \/  \/  \/  v  \/ 

o        o        o        o        o        o 

Burnt  lime  which  has  been  air-slaked  and  hydrated  lime 
which  contains  considerable  carbonate  are  not  recommended 


276  INSECTICIDES  AND  FUNGICIDES 

for  use  in  making  Bordeaux  unless  the  proportion  of  lime 
is  increased.  Calcium  carbonate  does  not  form  a  compound 
with  copper  sulphate. 

The  active  agent  in  killing  fungi  is  copper  sulphate,  but 
the  use  of  copper  sulphate  even  in  dilute  solution  is  attended 
with  so  much  danger  to  foliage  that  Bordeaux,  which  is  a 
suspension  of  an  insoluble  copper  salt  in  water,  is  far  pre- 
ferable. The  bluish-white  particles  are  distributed  over  the 
surface  of  leaves,  and  under  the  action  of  water  and  carbon 
dioxide  very  small  quantities  of  copper  sulphate  are  formed, 
sufficient  to  kill  fungous  spores  and  germ  tubes.  Calcium 
carbonate  is  also  formed. 

Under  certain  climatic  conditions,  such  as  long  periods  of 
damp  weather,  but  no  rain,  enough  copper  sulphate  may  be 
formed  to  burn  the  leaves.  Even  under  these  conditions, 
however,  the  presence  of  an  excess  of  lime  prevents  this 
danger.  The  formulas  call  for  more  lime  than  is  necessary 
to  form  the  compound  with  copper. 

Bordeaux  may  be  mixed  with  arsenicals — Paris  green  and 
lead  arsenate — to  good  advantage  so  as  to  have  both  an 
insecticide  and  a  fungicide  in  the  same  spray.  Paris  green  is 
benefited  by  this  mixing  because  the  excess  of  lime  neutralizes 
the  free  arsenous  acid  so  readily  formed  in  plain  Paris  green 
applications. 

(c)  Corrosive  Sublimate,  Mercuric  Chloride,  fIgCl2, 
is  a  very  powerful  fungicide  and  antiseptic.  Furthermore, 
it  is  very  poisonous  to  human  beings  and  should  be  used 
with  great  care.  A  solution  of  1  part  sublimate  to  one 
thousand  parts  of  water  is  a  common  strength  to  employ. 
Since  mercuric  chloride  corrodes  metal  the  solution  should 
be  made  in  a  wooden  pail  preferably.  Sometimes  it  is 
purchased  in  tablets  mixed  with  ammonium  chloride  which 
increases  the  solubility  of  the  mercuric  chloride  by  the  forma- 
tion of  a  double  mercurammonium  chloride,  HgCl2.(NH4Cl)2. 

(d)  Formaldehyde  is  a  gas,  CH2O,  at  ordinary  tempera- 
tures. It  dissolves  in  water  readily,  and  in  commerce  is 
sold  in  the  form  of  a  solution  containing  approximately 
38  per  cent,    by  weight.      Formalin    is    the    trade   name 


FUNGICIDES  277 

of  such  a  solution  made  by  one  German  firm  only.  It 
has  no  advantages  whatever  over  any  38  per  cent,  solu- 
tion made  by  other  reputable  manufacturers.  Formal- 
dehyde may  be  used  in  the  liquid  form  by  proper 
solution  or  in  the  gaseous  form  by  liberating  it  in  a  closed 
room.  The  evolution  of  formaldehyde  may  be  produced 
by  heating  the  solution  under  pressure;  by  simple  evapora- 
tion from  large  surfaces;  by  treatment  with  potassium  per- 
manganate whereby  part  of  the  formaldehyde  is  oxidized 
and  the  heat  of  oxidation  volatilizes  the  remainder;  or 
by  burning  the  so-called  formaldehyde  candles.  The  latter 
are  made  of  paraform  which  is  a  condensation  product 
of  formaldehyde  made  by  spontaneous  evaporation  of  the 
solution.  The  compound  is  supposed  to  be  trioxy methylene, 
(CH20)3.  On  heating  this  white  solid,  formaldehyde  is 
evolved. 

{e)  Lime-Sulphur  Boiled,  being  an  insecticide  as  well 
as  a  fungicide,  was  discussed  under  the  former  head 
(Section  204  II,  c). 

(/)  Lime-Sulphur  Self  Boiled  is  essentially  a  mechanical 
mixture  of  sulphur  and  slaked  lime.  It  is  prepared 
by  adding,  for  example,  6  pounds  of  sulphur,  finely 
ground,  to  6  pounds  of  lime  which  has  just  started  to 
slake.  The  mixture  is  stirred  and  more  water  added 
until  the  mass  boils,  due  to  the  slaking  lime.  The  boiling 
is  continued  five  or  ten  minutes  and  then  the  remainder 
of  the  water — to  equal  50  gallons  in  all — is  added.  This 
cools  down  the  mass.  The  violent  boiling  has  thoroughly 
mixed  the  sulphur  and  slaked  lime  and  formed  very  little 
calcium  sulphides.  But  at  the  strengths  applied  very  little 
sulphides  are  desired,  or  leaf  burning  results.  This  is  why 
the  boiling  is  checked  by  the  cold  water.  The  mixture  is  of 
course  a  suspension  and  must  be  applied  with  an  agitator. 
Lead  arsenate  and  some  other  insecticides  have  been  mixed 
with  the  self-boiled  lime-sulphur  with  good  results.  Some 
chemical  changes  take  place,  due  to  the  calcium  sulphides 
in  solution. 


278  INSECTICIDES  AND  FUNGICIDES 


EXERCISES 

1.  What  is  the  name  and  formula  of  the  acid  of  arsenic  from  which 
Paris  green  is  made? 

2.  Define  the  following  terms:  Alkaloid,  spore,  fungus,  arsenical,  emul- 
sion, fractional  distillation,  hydrocarbon,  viscous,  the  prefix  thio  and 
antiseptic. 

3.  What  arsenic  compound  found  in  sprays  is  soluble  in  hard  water? 

4.  Show  what  each  part  of  the  chemical  name  for  Paris  green  means. 

5.  Give  a  detailed  explanation  of  how  lead  arsenate,  kerosene  emulsion, 
Bordeaux  mixture  and  hydrocyanic  acid  gas  kill. 

6.  Show  by  calculation  that  100  parts  by  weight  of  sodium  cyanide  are 
equal  in  effectiveness  to  132  parts  by  weight  of  potassium  cyanide. 

7.  Mention  the  conditions  under  which  leaf  burning  caused  by  the  appli- 
cation of  an  insecticide  or  fungicide  might  result. 


REFERENCES 

Bur.  Ent.,  Bui.  No.  90,  Pt.  I,  U.  S.  Dept.  Agr.  Hydrocyanic  Acid  Gas 
Fumigation  in  California. 

Bur.  Ent.,  Bui.  No.  90,  Pt.  Ill,  U.  S.  Dept.  Agr.  Chemistry  of  Fumiga- 
tion with  Hydrocyanic  Acid  Gas. 

Bur.  Ent.,  Bui.  No,  116,  Pt.  IV,  U.  S.  Dept.  Agr.  Lime-Sulphur  as  a 
Stomach  Poison  for  Insects. 

Illinois  Agr.  Expt.  Sta.,  Bui.  No.  135.     Bordeaux  Mixture. 

Iowa  Agr.  Expt.  Sta.,  Research  Bui.  No.  12.  Chemical  Studies  of  Lime- 
Sulphur-Lead  Arsenate  Spray  Mixture. 

New  York,  Cornell  Agr.  Expt.  Sta.,  Bui.  No.  288.  Spray  Injury  In- 
duced by  Lime-Sulphur  Preparations. 

New  York,  Cornell  Agr.  Expt.  Sta.,  Bui.  No.  290.  Studies  of  the  Fungi- 
cidal Value  of  Lime-Sulphur  Preparations. 

New  York,  Geneva  Agr.  Expt.  Sta.,  Bui.  No.  329.  Chemical  Investiga- 
tions of  Best  Conditions  for  Making  Lime-Sulphur  Wash. 

Penna.  Agr.  Expt.  Sta.,  Bui.  No.  86.  Miscible  Oils:  How  to  Make 
Them. 

Penna.  Agr.  Expt.  Sta.,  Bui.  No.  110.  The  Control  of  Insects  and 
Diseases  Affecting  Horticultural  Crops. 

Penna.  Agr.  Expt.  Sta.,  Bui.  No.  115.    Concentrated  Lime-Sulphur  Spray. 


CHAPTER  XVI 
THE  GAS  ENGINE 

Although  not  strictly  a  factor  in  plant  growth,  the  gas 
engine  has  become  a  very  important  factor  in  farm  life. 
For  running  tractors  in  plowing  large  farms  rapidly  (Fig.  73), 
in  furnishing  power  for  pumping,  silage  cutting,  cream 
separating,  and  in  moving  products  to  market,  as  well  as 
providing  rapid  means  of  locomotion  for  the  modern  farmer, 
the  gas  engine  today  occupies  an  almost  essential  place  on 
many  farms.  On  this  account  a  short  discussion  of  the  prin- 
ciples of  combustion,  products  obtained,  fuels,  and  lubricants, 
should  fit  in  at  this  point.  The  subject  of  gas  engines  is  too 
large  a  one  to  treat  from  any  standpoint  except  the  chemical 
one  and  should  include  only  such  other  details  as  may  be 
necessary  to  fully  understand  the  chemistry  involved. 

206.  The  Gas  Engine. — The  gas  engine  is  an  appliance  for 
making  use  of  the  energy  developed  when  a  mixture  of  a 
combustible  gas  and  air  explodes.  When  gases  explode  a 
sudden  pressure  is  produced.  This  pressure  is  directed  against 
a  piston-head  and  the  movement  of  the  piston  is  trans- 
mitted to  a  wheel  by  a  connecting  rod.  In  a  steam  engine, 
steam  is  admitted  first  to  one  end  and  then  to  the  other 
end  of  the  cylinder.  This  moves  the  piston  back  and  forth 
and  by  means  of  the  connecting  rod  a  wheel  rotates.  In  a 
gas  engine  a  mixture  of  gas  and  air  is  admitted  to  one  end  of 
the  cylinder  and  at  the  proper  moment  is  exploded,  usually 
by  an  electric  spark.  The  pressure  thus  developed  drives 
the  piston  to  the  other  end  of  the  cylinder.  Gas  is  not 
exploded  on  the  other  end  of  the  piston  to  drive  it  back, 
but  the  momentum  of  a  heavy  fly-wheel  attached  to  the 
main  shaft  carries  the  piston  back  again.  In  one  type  of 
engine,  the  so-called  "four-cycle"  type,  the  explosion  comes 
at  every  other  inward  movement  of  the  piston,  or  once  every 
two  revolutions  of  the  fly-wheel.  It  is  called  four-cycle 
because  there  are  four  strokes  which  complete  the  cycle: 

(279) 


280 


THE  GAS  ENGINE 


An  outward  movement  of  the  piston  which  draws  gas  and 
air  into  the  cyHnder,  or  intake;  inward  movement  and 
explosion,  or  compression;  outward  movement  and  work, 
or  expansion;  and  inward  movement,  or  exhaust.  In  the 
other  type,  the  "two-cycle,"  the  explosion  comes  at  every 
inward  movement  of  the  piston,  or  once  every  revolution  of 
the  fly-wheel.  In  this  type  the  crank  case  is  air  tight,  so 
that  air  and  gas  can  be  admitted  to  the  outer  end  of  the 
cylinder.  A  by-pass  permits  the  mixture  to  go  to  the  inner 
end  of  the  cylinder  for  the  explosion.  At  the  outward  stroke 
the  gas  and  air  are  first  compressed  in  the  crank  case  and 


Fig.  73. — Gasoline  tractor  for  plowing. 

then  as  the  by-pass  is  opened  by  the  movement  of  the  piston, 
the  mixture  is  forced  into  the  inner  end  of  the  cylinder, 
driving  ahead  of  it  the  burned  gas  through  a  port.  At  the 
inward  movement  of  the  piston  the  mixture  is  compressed 
and  the  explosion  takes  place,  and  at  the  same  time  gas  and 
air  are  drawn  in  to  the  outer  end  of  the  cylinder;  then  the 
cycle  is  repeated. 

A  very  important  part  of  the  gas  engine  is  the  carburetor 
or  place  where  the  air  and  gas  are  mixed.  If  the  fuel  is  a 
liquid  at  ordinary  temperatures  it  is  necessary  to  vaporize 
it  before  an  explosive  mixture  can  be  obtained.  A  liquid 
like  gasgline  vaporizes  very  readily  and  it  is  only  necessary 


CRUDE  PETROLEUM  281 

to  convert  it  to  a  spray  in  the  carburetor.  The  inflowing 
air  evaporates  the  fine  particles  of  liquid  and  a  gas  mixture 
results.  Fuels  like  kerosene  which  do  not  vaporize  so  readily 
at  ordinary  temperatures,  should  be  heated  before  they  are 
admitted  to  the  carburetor,  in  order  to  develop  maximum 
power. 

The  mechanical  devices  for  admitting  gas  and  air  to  the 
carburetor,  for  regulating  the  inflow  of  explosive  mixtures 
to  the  piston,  for  removing  the  burned  gas,  and  for  the 
numerous  other  necessary  steps  in  the  development  of 
maximum  power  in  a  gas  engine  cannot  be  discussed  here. 
For  such  details  the  reader  is  referred  to  books  on  gas  engines. 
(See  reference  list  at  end  of  chapter).  For  the  present  pur- 
pose, however,  a  brief  description  of  fuels,  their  properties 
and  sources,  may  not  be  out  of  place. 

207.  Crude  Petroleum. — Crude  petroleum  is  the  source  of 
gas  engine  fuels.  It  is  usually  a  heavy,  dark,  oily  liquid 
with  peculiar  characteristic  odor,  and  found  in  porous  rocks 
at  a  depth  of  300  to  3700  feet  below  the  earth's  surface.  The 
decomposition  of  organic  matter  within  the  earth  is  supposed 
to  be  the  origin  of  it.  Since  petroleum  is  an  inflammable 
liquid  it  can  be  used  in  the  crude  state  as  a  fuel,  but  not  of 
course  in  a  gas  engine.  To  obtain  the  greatest  value  from 
this  material  it  is  necessary  to  separate  it  into  its  various 
components.  This  can  be  readily  accomplished  by  fractional 
distillation,  since  petroleum  is  essentially  a  mixture  of  par- 
affine  hydrocarbons  of  very  many  kinds.  There  are  other 
compounds  in  some  petroleum,  but  in  the  better  grades  of 
Pennsylvania  oils  from  which  the  refined  products  are  most 
easily  made,  these  compounds  are  present  in  very  small 
amounts  and  need  not  be  considered. 

The  paraffine  hydrocarbons  have  as  empyrical  formula 
CnH2n+2  and  run  from  methane,  CH4,  to  hexacontane, 
C60H122,  from  gases  through  liquids  to  solids.  The  more 
carbon  atoms  in  the  molecule  the  greater  the  density  and  the 
higher  the  boiling  point.  Without  going  into  the  details  of 
the  distillation  process  it  is  sufficient  to  say  that  the  crude 
petroleum  is  charged  into  large  stills  and  heated,  the  various 
hydrocarbons  coming  off  at  different  temperatures.      By 


282  THE  GAS  ENGINE 

changing  receivers  at  any  point  in  the  boiling  as  many 
fractions  can  be  obtained  as  desired. 

At  first  there  are  obtained  only  three  or  four  fractions,  the 
first  one  called  benzine  distillate  or  crude  naphtha  (some- 
times light  naphtha  and  heavy  naphtha),  with  a  density  of 
80°  to  58°  Be.^  Then  come  burning  oils  or  kerosene  with  a 
density  of  58°  to  43°.  Tar  or  residuum  is  left  in  the  stills. 
The  temperature  of  distillation  rises  gradually  to  300°  or 
400°  C.  From  the  crude  naphtha  several  colorless  fractions 
are  usually  obtained  by  distilling  again  and  purifying  with 
strong  sulphuric  acid  and  caustic  soda.  The  liquid  to  be 
thus  treated  is  agitated  with  sulphuric  acid  of  66°  Be., 
then  washed  with  water,  agitated  with  caustic  soda  of 
4°  to  10°  Be.,  and  finally  washed  with  water.  The 
acid  and  soda  decompose  or  dissolve  various  impurities 
and  coloring  matters  in  the  petroleum  products  other  than 
the  paraffine  hydrocarbons.  The  spent  acid  which  settles 
to  the  bottom  is  drawn  off  as  "sludge"  acid  and  is  used  in 
some  places  for  making  phosphatic  fertilizers.  The  various 
fractions  have  different  names,  not  always  uniform.  They 
are  arbitrary  at  best,  depending  on  the  density.  Some  of 
the  names  are  gasoline;  naphtha.  A,  B,  C,  grades;  benzine; 
petroleum  ether,  etc.  It  is  not  safe  to  buy  by  name  for  any 
special  purpose  but  by  specific  gravity  (Baume  scale)  or  by 
boiling  points. 

The  kerosene  is  redistilled  into  two  or  more  nearly  colorless 
fractions,  purified  with  acid  and  alkali  as  above  described, 
and  sold  as  burning  oils  of  various  "tests."-    Many  of  the 

'  Baum6.  This  is  an  arbitrary  standard  of  density  for  liquids.  Hydrom- 
eters are  graduated  for  liquids  heavier  and  lighter  than  water.  For  the 
former,  0°  on  the  Baum6  scale  is  where  the  instrument  sinks  in  pure  water, 
and  10°  in  a  10  per  cent,  solution  of  salt.  For  the  latter  0°  is  the  point 
to  which  the  hydrometer  sinks  in  a  10  per  cent,  salt  solution,  and  10° 
in  pure  water.  The  graduation  is  extended  uniformly  in  both  cases.  The 
temperature  is  17.5°  C. 

2  For  use  in  lamps  particularly,  kerosene  must  not  be  so  volatile  as  to 
cause  an  explosion  when  the  wick  is  lighted.  This  volatility  or  "flash 
point, "  as  it  is  called,  is  regulated  by  law.  The  flash  point  is  the  temperature 
at  which  kerosene  gives  ofif  enough  vapor  to  ignite  in  a  flash  over  the  surface. 
In  most  of  our  states  110°  F.  is  the  legal  flash  point.  Flash  tests  are  the 
determinations  which  are  made  to  show  what  the  flash  points  are.  Fire 
tests,  also  made  sometimes,  are  the  determinations  which  show  the  tem- 
perature at  which  the  vapor  will  burn  continuously.  The  fire  point  is 
usually  about  20°  F.  higher  than  the  flash  point. 


GASOLINE  .     283 

above  distillations  are  accomplished  with  steam,  as  the 
steam  distilled  products  are  of  better  grade  with  less  loss 
and  less  danger  of  decomposition  in  the  still. 

The  tar  left  in  the  stills  is  removed  and  destructively 
distilled,  yielding  hydrocarbons  of  much  higher  density  and 
greater  viscosity ;  some  even  being  solid  at  ordinary  tempera- 
tures. By  redistillation,  washing  with  sulphuric  acid  and 
caustic  soda,  and  chilling  and  pressing,  there  are  obtained 
heavy  oils  used  for  lubricating — called  lubricating  and 
parafiine  oils — paraffine,  vaseline,  and  coke. 

The  very  volatile  products  of  low  density  are  used  for 
solvents;  intermediate  products  for  fuel;  kerosene  for  light- 
ing purposes;  lubricating  oils  for  machinery;  paraffine  for 
candles;  vaseline  for  medicine;  and  coke  for  electric  light 
carbons. 

208.  Gasoline. — Originally  the  name  gasoline  was  applied 
to  a  fraction  whose  density  was  somewhere  between  90°  and 
80°  Be.,  but  now  the  product  sold  under  the  name  of  gasoline 
maybe  anything  from 90°  to  60°  Be.  or  even  less.  Most  of 
the  engine  gasoline  runs  from  65°  to  60°  Be.,^  specific  gravity 
0.718  and  0.737,  boiling  point  120°  to  150°  C.  It  is  a  mixture 
of  hydrocarbons,  having  no  constant  composition.  It  is 
possible  to  obtain  any  particular  density  by  mixing  light 
and  heavy  fractions.  The  same  result  may  be  secured  by 
uniting  a  very  light  product  with  a  very  heavy  one,  or  by 
uniting  two  of  more  nearly  equal  densities.  As  a  result  the 
mere  specific  gravity  or  Baume  reading  of  a  grade  of  gasoline 
does  not  tell  the  purchaser  just  what  he  is  getting.  If  a  single 
hydrocarbon  liquid,  having  a  density  of  65°  Be.,  is  just  suited 
to  a  certain  engine,  a  grade  of  material  would  not  be  as  well 
suited  which  consists  of  a  mixture  of  very  light  hydrocarbon 
with  very  heavy  hydrocarbon,  the  resultant  density  of  which 
is  65°  Be.  The  lighter  material  would  vaporize  too  rapidly 
and  explode  too  easily,  whereas  the  heavier  portion  would 
vaporize  very  slowly  or  too  slowly  to  make  a  proper  explosive 
mixture.     In  time  it  may  be  possible  to  buy  gasoline,  or 

1  Instead  of  saying  "65°  or  60°  B6.  gasoline"  it  is  usually  customary  to 
speak  of  it  as  "65  or  60  test"  gasoline. 


284  THE  GAS  ENGINE 

at  least  a  gas  engine  fuel,  which  has  its  constituents  guaran- 
teed, in  order  that  the  purchaser  may  obtain  whatever  grade 
he  wants  for  his  particular  purpose.  Density  alone  is  not  the 
best  test ;  a  fractional  distillation  test  should  also  be  made. 

It  is  important  in  using  a  gas  engine  to  have  the  proper 
amount  of  air  mixed  with  the  gasoline  vapor.  Too  much 
air  dilutes  the  mixture  and  reduces  the  power.  Too  little 
air  does  not  permit  of  complete  combustion,  and  this  also 
reduces  the  power  and  causes  waste  of  fuel.  Gasoline  being 
a  mixture  of  hydrocarbons  burns  to  carbon  dioxide  and 
water  when  there  is  enough  oxygen  present.  On  this  account 
the  exhaustion  should  not  take  place  indoors  for  the  large 
quantities  of  carbon  dioxide  eliminated  are  detrimental 
to  health.    The  following  may  be  taken  as  a  typical  reaction : 

2C8Hi8+2502  =  16C02+18H20. 

This  means  that  one  gallon  of  gasoline,  assuming  it  to  be 
octane,  CgHis,  64.8°  Be.,  will  require  about  1180  cubic  feet 
of  air  at  62°  F.  When  insufficient  oxygen  is  present  the 
products  of  combustion  are  different,  and  include  carbon. 
The  maximum  amount  of  heat,  and  consequently  power,  is 
developed  only  when  combustion  is  complete. 

209.  Lubricants. — ^The  purpose  of  a  lubricating  oil  is  to 
reduce  friction  between  moving  surfaces,  and  it  should 
have  sufficient  "body"  or  viscosity  not  to  be  squeezed  out 
from  between  the  surfaces.  Too  viscous  an  oil  will  cause 
friction  of  the  oil  itself  and  reduce  efficiency.  A  lubricating 
oil  should  not  be  so  volatile  that  it  will  not  last  under  the 
temperature  to  which  it  is  subjected.  The  flash  test  is  useful 
in  determining  this  point.  Neither  should  an  oil  have  any 
free  acid  present,  such  as  sulphuric  acid  if  a  hydrocarbon  oil ; 
fatty  acid,  usually  stearic,  if  an  animal  or  vegetable  oil.  The 
free  acid  corrodes  the  bearings. 

From  the  tar  or  residuum  left  in  the  first  distillation  of  crude 
petroleum  there  are  obtained  (Section  207)  a  series  of  lubri- 
cating oils  which  are  of  excellent  character,  and  better 
suited  for  most  machinery  than  animal  or  vegetable  oils, 
though  for  some  purposes  the  latter  are  better. 


REFERENCES  285 

This  is  not  the  place  to  discuss  the  various  grades  of 
lubricating  oils  and  their  properties  and  uses,  but  it  may  be 
well  to  mention  one  fact  and  that  is  the  necessity  of  using  a 
good  grade  of  oil  especially  adapted  for  gas  engine  cylinders. 
The  contact  surface  of  the  piston  in  the  cylinder  must  be 
lubricated,  of  course,  and  since  the  temperature  is  very 
high,  the  oil  must  be  of  a  character  that  does  not  readily 
carbonize  or  volatilize  under  the  action  of  heat.  An  oil 
whose  density  is  26°  to  28°  Be.,  with  a  flash  test  of  400°  to 
475°  F.,  has  been  recommended  for  some  engines.  Dealers 
in  engines  can  recommend  the  best  cylinder  oil  for  use  in 
their  particular  engine'. 

EXERCISES 

1.  In  what  respects  are  the  reactions  that  take  place  in  a  gas  engine 
like  those  that  take  place  in  a  plant? 

2.  Show  that  the  energy  made  in  a  steam  engine  has  its  source  in  the  sun. 

3.  Compare  the  products  of  combustion  of  a  hydrocarbon  when  sufficient 
air  is  present  to  the  combustion  of  the  same  material  when  insufficient 
air  is  present.     Which  yields  the  more  energy?     Why? 

4.  What  is  meant  by  \nscosity,  Baume,  coke,  density,  specific  gravity, 
paraffine,  benzine  and  work? 

5.  Distinguish  between  fractional  and  destructive  distillation. 

6.  Why  must  a  gas  engine  be  lubricated? 

7.  What  in  a  plant  corresponds  in  function  to  octane;  to  a  lubricating 
oil;  to  the  exhaust;  to  the  machine  itself? 

8.  How  many  liters  of  pure  oxygen  under  standard  conditions  are  neces- 
sary to  completely  use  1000  grams  of  pure  octane  by  combustion?  How 
many  liters  of  air  under  the  same  conditions  would  furnish  as  much  oxygen? 

9.  Suppose  in  Exercise  8,  10  per  cent,  of  the  fuel  forms  carbon,  how 
many  liters  of  air  under  standard  conditions  are  necessary  for  its  combustion? 
How  many  liters  of  exhaust  gases  are  formed  under  these  conditions? 

10.  For  what  two  reasons  should  a  room  in  which  a  gas  engine  is  running 
be  well  ventilated? 

REFERENCES 

Hirshfeld  and  Ulbricht.     Gas  power. 
Levin.     The  Modern  Gas  Engine  and  the  Gas  Producer. 
Redwood.     A  Treatise  on  Petroleum,  3d  ed.,  vol.  ii. 
Rogers  and  Aubert.     Industrial  Chemistry,  Chapter  XXIII. 
Whitman.     Gas  Engine  Principles. 


PART  III 

THE  ANIMAL 


CHAPTER  XVII 
THE  CHEMISTRY  OF  ANIMAL  PHYSIOLOGY 

The  highest  and  most  complex  products  of  the  farm  are 
animals  (Fig.  74).  Directly  or  indirectly  animals  are  de- 
pendent on  plants  for  their  sustenance.  There  are,  of 
course,  many  obvious  differences  between  plants  and  animals, 
but  they  are  both  living  things  that  reproduce  themselves. 
They  are  composed  largely  of  carbon  compounds;  that  is, 
they  are  organic  in  nature.  For  the  proper  elaboration  of 
these  compounds,  a  few  elements  are  necessary.  But, 
whereas  plants  absorb  only  soluble  inorganic  compounds  and 
from  them  build  up  their  tissue,  animals  absorb  compara- 
tively little  of  such  material  but  must  have  organic  food 
material  previously  elaborated  by  plants.  This  material 
is  taken  into  the  animal  and  made  soluble  before  being 
absorbed  and  rebuilt  into  animal  tissue. 

210.  Essential  Elements  for  Animals. — For  animals  there 
are  needed  in  compound  form  the  following  fifteen  elements : 
Carbon,  hydrogen,  oxygen,  phosphorus,  potassium,  nitrogen, 
sulphur,  calcium,  iron,  magnesium,  sodium,  chlorine,  iodine, 
silicon,  and  fluorine.  It  is  to  be  noted  that  the  last  five 
elements,  while  essential  for  animals,  are  not  essential  for 
plants. 

211.  Composition  of  the  Animal. — Like  the  plant,  the 
animal  is  composed  largely  of  water,  but  not  to  so  great  an 
extent.  The  average  amount  of  water  in  farm  animals  is 
not  far  from  50  per  cent.  In  man  it  is  about  70  per  cent. 
Of  the  dry  matter  of  steers  60  per  cent,  is  carbon,  14  per 

( 287 ) 


288      THE  CHEMISTRY  OF  ANIMAL  PHYSIOLOGY 

cent,  oxygen,  9  per  cent,  hydrogen,  6  per  cent,  nitrogen,  and 
11  per  cent.  ash.  This  analysis  may  be  taken  as  fairly 
representative.  It  shows  (cf.  Section  53)  that  there  is  a 
much  larger  proporton  of  carbon  to  oxygen  in  animals  than 


Fig.  74. — Farm  animals. 


in  plants,  and  more  nitrogen.  This  is  because  the  dry 
matter  of  animals  consists  mostly  of  fats  and  proteins, 
whereas  the  dry  matter  of  plants  consists  largely  of  carbo- 
hydrates and  crude  fiber.  The  cell  walls  of  plants  are  made 
of  cellulose,  but  the  cell  walls  of  animals  are  made  of  protein. 


MUSCULAR  TISSUE  289 

Table  XVII  shows  the  composition  of  various  farm  animals, 
expressed  for  the  most  part  on  the  same  basis  as  the  compo- 
sition of  plants  in  Table  I,  except  that  there  is  no  crude 
fiber  or  nitrogen-free  extract. 


Table  XVII. — Composition 

OF  Farm  Animals 

Contents  of 

Water 

Fat 

Protein 

Ash 

stomach  and  in- 

Kind of  animal. 

per  cent. 

per  cent. 

per  cent. 

per  cent 

testines,  per  cent. 

Fat  calf         .      . 

.     63.0 

14.8 

15.2 

3.8 

3.2 

Half  fat  ox  .      . 

51.5 

19.1 

16.6 

4.6 

8.2 

Fat  ox    .      .      . 

45.5 

30.1 

14.5 

3.9 

6.0 

Fat  Iamb      .      . 

47.8 

28.5 

12.3 

2.9 

8.5 

Normal  sheep    . 

57.3 

18.7 

14.8 

3.2 

6.0 

Half  fat  sheep  . 

50.2 

23.5 

14.0 

3.2 

9.1 

Fat  sheep     . 

43.4 

35.6 

12.2 

2.8 

6.0 

Normal  pig 

55.1 

23.3 

13.7 

2.7 

5.2 

Fat  pig  . 

41.3 

42.2 

10.9 

1.6 

4.0 

In  studying  the  animal  it  is  necessary  to  know  something 
of  the  various  parts  of  the  body,  their  general  composition, 
their  functions,  and  the  reactions  taking  place  in  them.  The 
animal  is  obviously  very  complex  in  its  structure  and  only 
the  very  general  points  of  physiology  can  be  touched  upon. 
For  further  information  the  reader  is  referred  to  any  good 
text  on  animal  physiology.    (See  references  at  end  of  chapter) . 

212.  Bones. — ^The  framework  of  the  body  about  which 
all  the  tissues  are  grouped,  and  which  serves  to  give  rigidity 
and  afford  protection  to  the  more  delicate  and  sensitive 
parts  is  composed  of  bones  and  is  called  the  skeleton. 
Chemically  bones  are  composed  of  protein  material  called 
osseous  tissue,  or  ossein,  permeated  with  tricalcium  phos- 
phate and  calcium  carbonate.  The  mineral  and  organic 
part  are  present  in  about  equal  proportions  (Section  160). 
Bones  are  hollow  to  give  greater  strength  to  them,  and  are 
filled  with  soft  material  called  marrow,  which  consists  largely 
of  fat  and  protein.  Blood-vessels  permeate  the  bones,  and 
the  marrow  is  supposed  to  be  the  source  of  the  red  blood 
corpuscles.  Fig.  75  illustrates  the  appearance  of  bone  tissue 
under  the  microscope. 

213.  Muscular  Tissue. — ^The  flesh  of  an  animal,  or  muscular 
tissue  is  composed  usually  of  bundles  of  cells  called  fibers 

19 


290       THE  CHEMISTRY  OF  ANIMAL  PHYSIOLOGY 


Fig.  75. — Transverse  section  of  bone.     Magnified.     (Sharpey.) 


Fig.  76. — A,  portion  of  a  medium-sized  human  muscular  fiber.  Magnified 
nearly  800  diameters;  B,  separated  bundles  of  fibrils,  equally  magnified; 
a,  a,  larger,  and  b,  b,  smaller  collections;  c,  still  smaller;  d,  d,  the  smallest 
which  could  be  detached.     (Gray.) 


CONNECTIVE  TISSUE  291 

(Fig.  76).  It  causes  motion  in  the  animal,  having  the 
power  of  contracting  and  expanding  when  stimulated 
by  the  nerves.  This  contraction  may  be  transmitted  to 
the  bones  and  cause  locomotion,  or  may  be  merely  a  rhyth- 
mical contraction  and  expansion,  causing  the  well-known 
movements  of  the  heart,  lungs,  and  other  organs.  The 
muscle  substance  is  composed  largely  of  proteins,  but  also  of 
some  glycogen,  dextrose,  potassium  phosphate,  and  nitrog- 
enous extractives.^  It  is  about  75  per  cent,  water  and 
25  per  cent,  solids.  The  principal  protein  is  myosinogen, 
liquid  in  living  muscle,  but  changing  to  solid  myosin  in 
dead  muscle.  Living  muscle  at  rest  is  alkaline  in  character; 
active  and  dead  muscle  are  slightly  acid  due  to  the  formation 
of  an  isomer  of  lactic  acid  called  sarcolactic  acid.  Muscles  are 
bathed  in  lymph  and  permeated  with  blood-vessels.  When 
a  muscle  does  work,  the  dextrose  is  oxidized  by  the  oxygen 
brought  to  it  in  the  blood  stream,  and  carbon  dioxide  is 
given  off.    Heat  is  also  developed  by  this  oxidation. 

214.  Fatty  Tissue. — Besides  the  fats  or  fixed  oils  which 
constitute  a  part  of  all  protoplasmic  material,  there  are  in 
animals  various  deposits  6f  fat  in  the  muscles,  bone  marrow, 
liver,  and  so-called  adipose  tissue  (Fig.  77).  The  latter  is  a 
mass  of  cells  each  composed  mainly  of  a  large  globule  of 
fat.  This  adipose  tissue  usually  lies  just  under  the  skin. 
Chemically,  fat  is  composed  for  the  most  part  of  glycerides 
of  stearic,  palmitic,  and  oleic  acids,  as  in  the  case  of  plants 
(Section  14,  et  seq.). 

215.  Epithelial  Tissue. — Epithelial  tissue  lines  all  the 
surfaces  of  the  body — the  skin  on  the  outside  and  the 
mucous  membrane  on  the  inside,  such  as  the  lining  of  the 
alimentary  canal  and  body  cavities.  Such  epithelial  cells 
as  the  hair,  nails,  hoofs,  etc.,  are  composed  largely  of  a 
protein  called  keratin  which  is  rich  in  sulphur.  Epithelial 
cells. of  the  mucous  membrane  are  largely  mucin,  a  protein 
which  gives  this  tissue  its  viscid  character. 

216.  Connective  Tissue. — This  material  serves  to  bind 
together  the  various  body  parts,  and  composes  the  tendons, 

•  Nitrogen  compounds,  not  proteins,  soluble  in  water. 


292       THE  CHEMISTRY  OF  ANIMAL  PHYSIOLOGY 

cartilage,  and  such  substances.  Collagen  and  elastin  are 
two  proteins  contained  in  connective  tissue.  Gelatine  can 
be  prepared  from  collagen  by  boiling  it  in  water. 


Fig.  77. — Adipose  tissue,  highly  magnified,     a,  star-like  appearance,  from 
crystallization  of  fatty  acids.     (Gray.) 

217.  Blood. — This  liquid  serves  to  carry  nutrient  material 
to  all  parts  of  the  body,  supplying  the  various  tissues  with 
what  they  need  for  growth  and  repair.  It  also  serves  to 
carry  away  the  waste  products  of  metabolic  activity.  The 
blood  may  be  compared  roughly  to  the  sap  of  plants  in  so 
far  as  it  supplies  soluble  food  material  to  various  parts  of  the 
living  organism.  The  sap  of  plants,  it  will  be  remembered 
(Section  55),  is  forced  through  tracheae  up  the  stem  and 
into  the  leaves  by  osmotic  pressure  or  surface  tension,  or  a 
combination  of  both;  whereas  the  blood  is  forced  through 
a  system  of  open  canals  or  vessels  to  all  parts  of  the  animal 
body  by  the  pressure  of  a  pump  which  is  called  the  heart. 
A  rhythmic  expansion  and  contraction  of  muscles  around  the 
heart  pull  the  blood  in  and  force  it  out,  thus  keeping  up  a 
continuous  circulation  of  blood  through  the  vessels.  The 
main  channels  which  bring  blood  to  the  heart  are  called  veins, 
while  those  carrying  blood  away  from  the  heart  are  called 


BLOOD  293 

arteries.  All  the  tissues  of  the  body  are  penetrated  by  a 
system  of  very  fine  blood-vessels  called  capillaries,  and  it  is 
through  the  walls  of  these  capillaries  that  the  nutrient 
material  passes  and  thus  feeds  the  cells  of  the  tissues. 

Physically,  blood  is  an  opaque,  red  liquid  consisting  of  a 
clear  colorless  solution  called  plasma  holding  in  suspension 
several  kinds  of  solids,  one  of  them  red  in  color.  These 
red  colored  particles  are  so  numerous  that  they  give  the 
blood  a  red  appearance.  The  suspended  solids  are  red 
corpuscles,  white  corpuscles  and  some  other  small  bodies 
which  need  not  be  considered. 

(a)  Plasma  is  a  clear,  transparent,  colorless  or  slightly 
yellow,  partly  viscid  liquid,  consisting  largely  of  water  which 
holds  in  solution  or  in  suspension  proteins,  fats,  dextrose, 
lecithin,  mineral  salts,  urea,  uric  acid,  enzymes,  and  gases. 
The  proteins  are  principally  serum  albumin,  which  is  the 
most  important  constituent,  and  is  probably  the  source  of  the 
body  proteins.  Fibrinogen  is  another  protein,  and  although 
not  present  in  a  large  amount,  is  very  important.  This  will 
be  discussed  later  under  coagulation.  Fats  are  present  in 
minute  globules.  The  inorganic  salts  are  mostly  sodium  and 
potassium  chlorides,  carbonates,  sulphates  and  phosphates, 
together  with  calcium  and  magnesium  phosphates.  The 
reaction  of  the  blood  is  slightly  alkaline,  because  of  sodium 
carbonate  and  phosphate.  Urea  and  uric  acid  are  waste 
products. 

(6)  Red  Corpuscles,  Erythrocytes,  occur  in  the  blood  to 
the  extent  of  about  5,000,000  per  cubic  millimeter  in  man. 
They  are  disk-  or  bell-shaped,  about  7  5  microns  in  diameter 
(0.0075  mm.)  and  about  2  microns  thick  (0.002  mm.)  (Fig.  78). 
They  consist  of  a  framework  of  protein  material  called 
stroma  and  coloring  matter  called  haemoglobin.  The  latter 
compound  can  combine  with  oxygen,  carbon  monoxide,  and 
some  other  gases.  It  will  crystallize,  acts  as  a  weak  acid, 
and  is  composed  of  a  protein  called  globin  and  an  iron  com- 
pound which  is  the  real  coloring  matter.  Haemoglobin  when 
combined  with  oxygen  is  called  oxyhaemoglobin.  The  union 
is  a  weak  chemical  one  in  the  proportion  of  one  molecule 
of  haemoglobin  to  one  molecule  of  oxygen.     The  union  is 


294       THE  CHEMISTRY  OF  ANIMAL  PHYSIOLOGY 

apparently  a  function  of  the  iron,  one  atom  of  iron  combining 
with  two  atoms  of  oxygen.  The  oxygen  can  be  removed  by 
means  of  reducing  agents,  by  merely  passing  a  neutral  gas 
like  nitrogen  through  a  solution  containing  haemoglobin,  or 
by  exposure  to  a  vacuum.  Haemoglobin  is  darker  red,  more 
purplish  in  color,  than  is  oxyhsemoglobin,  which  is  bright 
red.  Blood  which  flows  in  the  veins  is  darker  in  color  than 
that  which  flows  in  the  arteries,  there  being  more  haemoglobin 
in  the  veins  and  more  oxyhaemoglobin  in  the  arteries.  Haemo- 
globin in  the  form  of  oxyhaemoglobin  is  the  oxygen  carrier 
of  the  blood.     As  was  noted  above,  carbon  monoxide  will 


Fig.  78. — Human  red  blood  corpuscles.  Highly  magnified,  a,  seen  from 
the  surface;  b,  seen  in  profile  and  forming  rouleaux  ;  c,  rendered  spherical 
by  water;  d,  rendered  crenate  by  salt  solution.     (Gray.) 


unite  with  haemoglobin  and  the  combination  is  stronger  than 
the  combination  of  oxygen  with  haemoglobin.  Hence  in  an 
atmosphere  containing  carbon  monoxide,  the  oxygen  is 
driven  out  of  combination  with  the  haemoglobin  and  the 
carbon  monoxide  takes  its  place.  This  is  the  cause  of  carbon 
monoxide  poisoning,  since  the  carrying  of  oxygen  by  the 
haemoglobin  is  a  very  necessary  function  of  the  blood. 

(c)  White  Corpuscles,  Leucocytes,  occur  in  the  blood 
of  man  to  the  extent  of  about  5000  to  10,000  to  the  cubic 
millimeter.  They  are  more  variable  in  size  and  form  than 
the  red  corpuscles,  being  4  to  13  microns  in  diameter  (0.004 
to  0.013  mm.).     They  can  move  by  their  own  processes, 


BLOOD 


295 


P6X) 


being  somewhat  amoeboid  in  character  (Fig.  79).  They  can 
pass  through  the  walls  of  the  capillaries  and  wander  through 
the  tissue  fluids.  These  leucocytes  are  composed  of  proteins, 
glycogen,  lecithin,  fat,  and  phosphates.  They  are  said  to 
serve  as  blood  scavengers,  carry- 
ing away  and  absorbing  undis- 
solved substances  in  the  blood 
such  as  bacteria.  Apparently 
whenever  a  wound  gives  entrance 
to  bacteria  the  white  corpuscles 
swarm  to  that  place  arjd  help  to 
destroy  them.  Although  this  fact 
has  not  been  definitely  proved,  it 
is  still  a  reasonable  belief. 

(d)  Coagulation. — On  expos- 
ure to  the  air  blood  clots  or  coagu- 
lates, and  there  is  formed  a  mass 
of  corpuscles  matted  together 
with  a  fibrous  substance.  The 
cause  of  this  clotting  is  not  defi- 
nitely known,  but  the  theory  has 
been  advanced  that  an  enzyme 
with  the  help  of  a  calcium  salt 
acts  on  fibrinogen,  a  soluble  pro- 
tein, changing  it  to  fibrin,  an 
insoluble  protein.  Fibrin  is  a 
white,  fibrous  material  which  en- 
tangles the  corpuscles  into  a  clot. 
The  liquid  remaining  after  the 
clot  forms  is  called  serum,  and  is 
merely  plasma  without  the  fibrin- 
ogen. By  beating  fresh  drawn 
blood  the  fibrin  can  be  obtained 
free  from  corpuscles.    The  speed 

of  coagulation  is  hindered  by  cold,  by  a  10  per  cent,  solution 
of  ammonium  oxalate  or  of  sodium  chloride.  It  is  hastened 
by  heat,  ferric  chloride,  and  alum.  Speed  of  coagulation 
also  varies  with  animals.  The  blood  of  horses  clots  very 
slowly. 


Fig.  79. — Small  blood-vessel, 
showing  how  leucocytes  pene- 
trate the  wall.    (G.  Bachman.) 


296       THE  CHEMISTRY  OF  ANIMAL  PHYSIOLOGY 


(e)  Gaseous  Exchange  in  the  Blood. — Reference  has 
been  made  occasionally  to  the  fact  that  the  blood  in 
one  way  or  another  carries  oxygen  and  carbon  dioxide. 
The  oxygen  is  necessary  to  oxidize 
dextrose  and  supply  energy  to  the 
various  tissues.  Carbon  dioxide  is  a 
result  of  the  oxidation  of  dextrose  and 
must  be  eliminated.  The  lungs  are  the 
seat  of  exchange  between  the  oxygen 
and  the  carbon  dioxide.  They  are  a 
mass  of  tissue  containing  very  many 
minute  cells  or  alveoli  surrounded  by 
capillaries.  The  venous  blood  coming 
into  the  right  side  of  the  heart  is  charged 
with  carbon  dioxide.  It  is  forced  from 
there  to  the  lungs  where  carbon  dioxide 
is  given  off  and  oxygen  taken  in.  This 
renewed  blood  passes  then  to  the  left 
side  of  the  heart  where  it  is  discharged 
into  the  arterial  system.  Fig.  80  gives 
in  diagrammatic  form  the  circulation 
of  the  blood. 

The  lungs  contract  and  expand  by 

involuntary    muscular  effort   as  they 

exhale   and   inhale   air.     From   Table 

XVIII,  which    gives  the  composition 

of  100  volumes  of  inspired  and  expired 

air,  it  is'  to  be  noted  that  the  inspired  air  is  richer  in  oxygen 

than  the  expired  air,  and  contains  much  less  carbon  dioxide 

and  water. 

Table  XVIII. — Composition  of  Air 

100  volumes 
Inspired  air.  Expired  air. 

Oxygen -20.80             Oxygen 16.02 

Carbon  dioxide.            .      .     trace              Carbon  dioxide             .      .  4.38 

Nitrogen 79.20            Nitrogen 79.60 

Water     .......  variable  Water    .      .      .      .      .     saturated 

Organic  matter      .      .      .  trace 

From  Table  XIX,  which  gives  the  composition  of  100 
volumes  of  arterial  and  venous  blood  at  0°  and  760  mm. 


Fig.  80. — Diagram  of 
blood  circulation:  L, 
lung  capillaries;  c,  other 
capillaries;  r,  rV,  right 
compartments  of  heart; 
I,  IV,  left  compartments 
of  heart. 


BLOOD  297 

pressure  it  can  be  seen  that  the  arterial  blood  contains  more 
oxygen  and  less  carbon  dioxide  than  the  venous  blood. 

Table  XIX. — Composition  of  Gases  in  Blood 

100  volumes 

Arterial.  Venous. 

Oxygen 20  12 

Nitrogen 1  to  2  1  to  2 

Carbon  dioxide 40  45 

The  blood  going  into  the  lungs  through  the  capillaries  is 
charged  with  carbon  dioxide  but  it  does  not  contain  its  full 
quota  of  oxygen.  The  inspired  air  with  which  this  blood 
comes  in  contact  contains  on  the  other  hand  an  excess  of 
oxygen  and  little  or  no  carbon  dioxide.  Consequently, 
oxygen  passes  through  the  capillary  walls,  dissolves  in  the 
blood  plasma,  and  then  combines  with  the  haemoglobin  to 
form  oxyhaemoglobin.  Carbon  dioxide  meanwhile  has  been 
carried  in  the  blood  in  the  form  of  sodium  bicarbonate  and 
dissolved  to  a  slight  extent  in  the  blood  plasma.  The  dis- 
solved carbon  dioxide  passes  through  the  capillary  walls 
into  the  lung  cells  and  with  the  reduction  in  the  amount 
of  dissolved  carbon  dioxide,  sodium  bicarbonate  breaks  up 
into  sodium  carbonate  and  carbon  dioxide,  the  latter  pass- 
ing into  the  lung  cells,  as  above  described. 

The  blood,  now  charged  with  oxygen  and  containing  less 
carbon  dioxide,  passes  to  the  tissues  where  oxygen  is  needed. 
The  oxyhaemoglobin  now  breaks  up,  oxygen  dissolving  in  the 
plasma  and  passing  through  the  capillaries.  It  oxidizes 
dextrose  with  the  elimination  of  carbon  dioxide,  which  passes 
through  the  capillaries,  first  dissolving  in  the  plasma  and 
then  combining  with  the  sodium  carbonate  to  form  sodium 
bicarbonate. 

The  above  gaseous  exchange  in  the  lungs  and  in  the 
tissues  is  caused  by  a  difference  in  the  pressure  of  oxygen 
and  carbon  dioxide,  and  is  the  result  of  mass  action  as  can 
be  easily  seen  from  the  following  reversible  equations: 

Hsemoglobin  +  Oz  ll^  Oxyhsemoglobin 
2NaHC0.  X  NajCOj  +  CO2  +  H2O. 


298       THE  CHEMISTRY  OF  ANIMAL  PHYSIOLOGY 

The  carbon  dioxide  in  the  veins  is  under  greater  pressure 
than  the  carbon  dioxide  in  the  inspired  air.  Hence  the 
plasma  loses  carbon  dioxide  and  sodium  bicarbonate  breaks 
up.  The  partial  pressure  of  the  oxygen  dissolved  in  the 
plasma  is  less  than  that  of  the  oxygen  in  the  lungs.  Hence 
more  oxygen  is  dissolved  by  the  plasma  and  consequently 
a  combination  of  oxygen  with  haemoglobin  takes  place. 

Chemically  one  volume  of  oxygen  produces  one  volume  of 
carbon  dioxide,  but  in  the  case  of  animal  respiration  the 
amount  of  carbon  dioxide  evolved  is  normally  less  than  the 
amount  of  oxygen  absorbed.  This  is  because  some  oxygen 
is  used  to  oxidize  the  hydrogen  of  fat  to  water  and  to  form 
waste  products  from  proteins  like  urea.  Therefore  it  does 
not  appear  as  carbon  dioxide.  The  ratio  of  carbon  dioxide 
to  ox^'gen  by  volume  is  called  the  respiratory  quotient. 

218.  Lymph. — The  tissues  of  the  body  are  all  bathed  in  a 
liquid  called  lymph,  or  tissue  fluid,  which  serves  to  bring 
nutrient  material  in  direct  contact  with  the  tissue  cells  and 
to  carry  waste  products  away  from  the  tissue  cells.  The 
various  tissues  are  all  in  a  constant  state  of  building  up  and 
tearing  down.  Changes  are  constantly  taking  place.  New 
cells  are  forming  and  old  ones  wearing  out.  The  blood 
serves  as  the  fluid  which  carries  nutrient  material  from 
one  part  of  the  body  to  another  and  transports  waste 
products  of  metabolism  for  elimination.  It  is  carried  within 
the  walls  of  the  blood-vessels — veins,  arteries,  and  capillaries. 
Water,  soluble  compounds,  and  leucocytes  can  pass  through 
the  walls  of  the  capillaries,  and  this  fluid,  which  is  practically 
blood  plasma,  constitutes  the  lymph. 

Not  only  are  the  tissues  bathed  in  lymph  but  the  tissue 
spaces  unite  to  form  lymph  vessels  which  are  provided  with 
valves  at  frequent  intervals  to  prevent  the  fluid  from  flowing 
backward.  These  vessels  permeate  the  body  in  every  direc- 
tion in  a  network,  and  combine  sooner  or  later  into  the 
thoracic  duct  (Fig.  82,  th.d.),  a  large  lymph  vessel  running 
through  the  left  side  of  the  centre  of  the  body  and  emptying 
into  the  venous  system  at  the  left  side  of  the  base  of  the 
neck.  At  intervals  along  the  lymph  vessels  are  enlargements 
called  lymph  glands  which  serve  among  other  things  as  a 
principal  source  of  white  corpuscles. 


ANIMAL  COMPOUNDS  299 

Pressure  caused  by  blood  plasma  being  forced  out  of  the 
capillaries,  possibly  contraction  of  lymph  vessels,  and  par- 
ticularly muscular  exercise,  all  serve  to  force  lymph  along 
its  vessels  so  that  a  continuous- stream  is  poured  into  the 
veins  from  the  thoracic  duct. 

Lymph  being  essentially  blood  plasma  is  a  clear  to  opales- 
cent liquid,  slightly  alkaline  in  character,  containing  proteins, 
dextrose,  sodium  chloride  and  carbonate,  some  other  salts, 
white  corpuscles,  and  a  small  amount  of  fibrinogen.  It 
also  contains  oxygen  and  carbon  dioxide  dissolved  in  it, 
although  part  of  the  latter  is  combined  with  sodium  car- 
bonate. The  proportion  of  the  various  constituents  is  not 
quite  the  same  as  that  in  blood  plasma  and  varies  from 
one  part  of  the  body  to  another  according  to  the  needs  of 
the  body. 

219.  Animal  Compounds. — Many  of  the  animal  compounds 
are  the  same  as  those  in  plants,  but  there  are  some  differences, 
enough  to  w-arrant  a  brief  review  of  the  subject.  In  this 
discussion,  of  course,  no  attention  is  paid  to  compounds 
eaten  by  the  animal  for  food — only  those  compounds 
actually  absorbed  and  utilized  by  the  animal.  For  conveni- 
ence in  comparison,  the  same  order  will  be  observed  as  in 
Chapter  I  on  Plant  Compounds. 

(a)  Carbohydrates.-— Of  the  many  carbohydrates  known 
only  three  are  of  importance  in  the  animal. 

1.  Dextrose,  already  described.  Section  3.  It  is  found  in 
blood,  liver,  muscles,  and  other  tissues,  serving  as  a  source  of 
energy  by  its  oxidation,  and  also  as  a  source  of  fat  (Section 
224,  a). 

2.  Glycogen,  Animal  Starch  (C6Hio05)n- — It  is  a  white, 
amorphous,  tasteless  powder,  dissolving  in  water  to  an 
opalescent  solution,  and  giving  a  dark  red  color  with  iodine. 
On  hydrolysis  with  mineral  acids  or  with  amylolytic  enzymes 
it  yields  dextrose.  The  liver  is  the  principal  repository  of 
glycogen,  containing  from  1  to  4  per  cent.  The  liver  produces 
glycogen  from  dextrose,  levulose,  and  probably  galactose, 
the  forms  of  soluble  carbohydrates  absorbed.  As  needed  by 
the  body  the  liver  reproduces  dextrose.  Glycogen  is  also 
found  in  the  muscles  to  a  maximum  extent  of  1  per  cent. 


300       THE  CHEMISTRY  OF  ANIMAL  PHYSIOLOGY 

Like  starch  in  the  plant,  glycogen  in  the  body  is  the  concen- 
trated, dehydrated  form  of  storage  carbohydrate  material  in 
the  animal. 

3.  Lactose. — ^This  is  found  in  milk  and  will  be  described 
in  Section  228,  a. 

4.  Cellulose  and  Crude  Fiber  are  not  found  in  animals  as  in 
plants. 

(6)  Fats. — The  fats  are  very  much  the  same  as  in  plants. 
Their  general  properties  are  the  same,  but  there  are  a  few 
animal  fats  and  oils  which  deserve  mention. 

1.  Tallow  is  the  name  given  to  certain  animal  fats,  more 
or  less  hard  in  character  and  extracted  or  "rendered"  from 
adipose  tissue  by  melting  out  the  fat  to  free  it  from  the 
protein  membranes.  It  is  almost  white  when  pure  and  nearly 
tasteless.  It  is  composed  of  mixed  glycerides  of  stearic, 
palmitic,  and  oleic  acids  in  varying  proportions,  the  com- 
mercial grades  usually  containing  free  fatty  acids  due  to 
hydrolysis  of  the  glycerides.  Beef  tallow  or  beef  fat  is  softer 
than  mutton  tallow.  The  former  is  used  for  making  oleomar- 
garine (Section  232)  and  as  an  adulterant  of  lard  in  addition 
to  its  use  as  a  food.  The  latter  is  employed  in  the  making 
of  soap,  candles,  and  lubricants  besides  being  used  as  a  food. 

2.  Lard  is  the  fat  of  pigs,  and  is  obtained  by  rendering, 
as  in  the  case  of  tallow.  It  is  composed  of  the  glycerides  of 
stearic,  palmitic,  oleic,  myristic,  lauric,  linoleic,  and  possibly 
linolenic  acids. 

3.  Neatsfoot  Oil  is  made  from  the  feet  and  shin  bones  of 
cattle  by  boiling  them  in  water.  The  oil  rises  to  the  surface  and 
is  skimmed  off.  It  is  pale  yellow  in  color,  consisting  chiefly 
of  olein  with  some  palmitin  and  stearin.  In  leather  dressing 
and  as  a  lubricant  it  finds  its  chief  uses. 

4.  Codliver  Oil  is  extracted  from  the  liver  of  the  cod,  pure 
varieties  being  used  in  medicine,  and  other  kinds  in  tanning. 
Its  composition  is  very  complex,  containing  in  addition  to 
the  glycerides  of  myristic,  palmitic,  stearic,  oleic,  and  erucic 
acids,  fats  of  two  new  acids. 

5.  Menhaden  Oil  is  obtained  from  the  whole  body  of  the 
menhaden  fish  by  boiling  in  water  and  expressing.  It  finds 
various  uses,  as  in  soap  making  and  tanning. 


ANIMAL  COMPOUNDS  301 

6.  Sperm  Oil  is  not  a  true  oil,  being  a  liquid  wax  (Section 
21),  or  compound  of  fatty  acids,  principally  oleic,  with 
monohydric  alcohols.  It  is  obtained  from  the  head  cavities 
of  the  sperm  whale.  On  cooling  it  deposits  crystals  of  sperm- 
aceti, a  solid  wax.  Sperm  oil  is  a  most  excellent  lubricant. 
Spermaceti  is  used  in  making  candles  and  in  medicine. 

7.  Beeswax  is  the  substance  from  which  honey-comb  is 
made,  being  manufactured  by  the  bees.  It  is  a  tough,  com- 
pact mass,  yellow  or  brownish  in  color.  It  is  not  greasy 
to  the  touch.  In  composition  it  is  a  wax,  containing  com- 
pounds of  palmitic,  cerotic,  and  melissic  acids  with  mono- 
hydric alcohols,  and  in  addition  some  higher  hydrocarbons. 

8.  Volatile  Oils  are  not  found  in  animals. 

(c)  Nitrogenous  Compounds. — These  are  for  the  most 
part  proteins,  which  differ  somewhat  from  plant  proteins. 
Most  of  the  knowledge  of  proteins  is  derived  from  a  study 
of  these  compounds  in  the  animal.  They  have  been  classified, 
their  properties  observed  and  tests  described,  but  their 
study  is  too  complex  and  technical  for  a  work  of  this  kind. 
As  occasion  arises  various  proteins  will  be  named  and  briefly 
described.  Other  nitrogenous  compounds,  as  amino-a(;ids 
and  ammonium  compounds,  occur  as  transition  products. 

(d)  Organic  Acids  are  not  a  normal  part  of  the  animal 
body,  except  as  by-products  of  metabolic  activity,  as,  for 
example,  sarcolactic  acid  in  active  muscle,  and  uric  acid — 
waste  material  in  the  blood. 

(e)  Compounds  of  the  Inorganic  Elements. — In  the 
plant  inorganic  compounds  exist  merely  as  transitory  food 
materials  absorbed  by  the  roots.  The  so-called  inorganic 
elements  are  combined  organically  for  use  by  the  plant 
either  as  an  integral  part  of  its  tissue  or  as  a  sort  of  helping 
compound  for  tissue  formation.  In  the  animal,  however, 
inorganic  compounds  play  a  very  important  part.  They  can 
best  be  taken  up  by  elements. 

1.  Compounds  of  Phosphorus.  —  Calcium  phosphate, 
Ca3(P04)2,  exists  in  bones  and  teeth,  and  CaH4(P04)2  in 
the  tissue  fluids.  In  the  bones  and  teeth  it  gives  solidity 
to  the  organs.     It  is  associated  with  magnesium  phosphate, 

Mg3(P04)2. 


302       THE  CHEMISTRY  OF  ANIMAL  PHYSIOLOGY 

Sodium  phosphate,  Na2HP04,  is  found  in  all  the  solids 
and  fluids  of  the  body,  giving  an  alkaline  reaction  to  the 
latter.  It  is  associated  with  potassium  phosphate,  K2HPO4, 
with  similar  properties. 

2.  Compounds  of  Potassium. — Potassium  chloride,  KCl, 
occurs  together  with  sodium  chloride  in  all  the  tissues  and 
fluids  of  the  body,  being  present,  however,  to  a  greater 
extent  in  the  tissues  than  in  the  fluids. 

Potassium  carbonate,  K2CO3,  is  found  with  potassium 
phosphate,  which  is  mentioned  above. 

3.  Compounds  of  Calcium. — Calcium  phosphate,  mentioned 
above. 

Calcium  carbonate,  CaCOs,  occurs  together  with  calcium 
phosphate  in  various  parts  of  the  body,  and  fulfills  appar- 
ently the  same  functions.  In  the  tissue  fluids  it  occurs  as  a 
bicarbonate,  CaH2(C03)2- 

Calcium  fluoride,  CaFa,  is  found  in  the  bones  and  teeth. 

4.  Compounds  of  Iron  are  organic  in  nature,  occurring  in 
haemoglobin,  in  the  lymph,  bile,  gastric  juice,  and  in  the 
coloring  matter  of  the  eyes,  hair,  and  skin. 

5.  Compounds  of  Sodium. — Sodium  chloride,  NaCl,  is 
present  in  all  the  tissues  and  fluids  of  the  body,  particularly 
in  the  latter.  The  blood  contains  0.6  per  cent.,  lymph 
0.5  per  cent.  Its  function  apparently  is  to  maintain  osmotic 
equilibrium  between  the  cells  and  the  fluids  of  the  body, 
regulating  the  intake  of  water  to  the  former.  In  pure  water 
the  tissue  cells  swell  rapidly  and  die.  The  presence  of  sodium 
chloride  in  water  prevents  too  rapid  entrance  of  water 
to  the  cells.  On  this  account  in  investigating  living  tissue 
it  is  customary  to  use  a  physiological  salt  solution  which 
is  a  0.6  per  cent,  solution  of  sodium  chloride.  Sodium 
chloride  is  also  the  source  of  chlorine  for  potassium  chloride 
mentioned  above  and  also  for  the  hydrochloric  acid  of  the 
gastric  juice  mentioned  below. 

Sodium  phosphate,  mentioned  above. 

Sodium  carbonate,  Na2C03,  found  together  with  sodium 
phosphate,  and  serves  also  to  give  alkalinity  to  the  tissue 
fluids.  When  combined  with  carbon  dioxide  it  exists  in  the 
form  of  sodium  bicarbonate,  NaHCOs. 


REFERENCES  303 

6.  Compounds  of  Chlorine. — Sodium  chloride  and  Potassium 
chloride,  mentioned  above. 

Hydrochloric  acid,  HCl,  is  found  in  small  amounts  in  the 
gastric  juice  of  the  stomach  where  it  aids  in  the  enzyme 
activity  of  digestion. 

7.  Compounds  of  Iodine  are  found  in  organic  form  in  the 
thyroid  gland  of  man. 

8.  Compounds  of  Silicon  occur  in  organic  form  in  the  hair. 

EXERCISES 

1.  Which  of  the  following  are  found  only  in  plants,  only  in  animals,  in 
both:  Silicon,  enzymes,  iron,  glycogen,  urea,  crude  fiber,  ossein,  fibrinogen, 
lymph,  fats? 

2.  Do  animals  or  plants  contain  more  of  each  of  the  following:  Water, 
carbohydrates,  fats,  proteins  and  ash? 

3.  Are  bones  living  material?     Why  or  why  not? 

4.  Suggest  a  possible  function  for  each  of  the  substances  found  in  muscle 
tissue. 

5.  Mention  the  differences  in  the  properties  of  the  protein  that  constitutes 
epithelial  tissue  and  that  which  constitutes  muscle  tissue. 

6.  What  is  the  difference  between  blood  and  lymph?  What  is  the  chief 
function  of  each? 

7.  Suppose  blood  was  lacking  in  each  of  the  following,  what  could  it  not 
do:  Leucocytes,  a  calcium  salt,  haemoglobin,  sodium  bicarbonate,  dis- 
solved carbon  dioxide,  dissolved  oxygen,  dextrose,  amino-acids,  fibrinogen 
and  urea? 

8.  What  is  the  chief  function  of  each  of  the  following  in  animals:  Glyco- 
gen, protein,  fat,  compounds  of  metallic  elements,  and  water? 

9.  Show  by  equations  and  calculations  that  the  respiratory  quotient  of 
carbohydrates  is  equal  to  1  and  that  of  fats  to  0.7. 

10.  Can  you  suggest  any  value  of  the  respiratory  quotient? 

REFERENCES 

Brubaker.     Text  Book  of  Physiology. 
Hawk.     Practical  Physiological  Chemistry. 
Smith.     Manual  of  Veterinary  Physiology. 
Starling.     Human  Physiology. 


CHAPTER  XVIII 
FOOD  AND  DIGESTION 

One  of  the  principal  differences  between  plants  and 
animals  is  the  manner  of  food  absorption.  Plants  must 
have  their  food  dissolved  on  the  outside  before  they  can  take 
it  into  their  circulatory  system.  Animals  can  take  in  in- 
soluble food  and  make  it  soluble  within  themselves  before 
absorbing  it  into  their  circulatory  system.  For  a  proper 
understanding  of  the  principles  of  feeding  it  is  necessary  to 
know  something  of  the  chemical  processes  by  which  foods 
are  made  soluble  in  the  animal  and  of  their  functions  after 
absorption. 

220.  Food. — Sherman  defines  food  as  "those  substances 
which  supply  the  body  either  with  material  needed  for  its 
substance,  or  with  energy  for  its  activities."  Sometimes  a 
distinction  is  made  between  the  food  of  human  beings  and 
the  food  of  animals.  This  is  a  distinction  in  terminology 
only,  food  of  domestic  animals  being  called  feed  as  distinct 
from  food  which  is  applied  to  human  foods  only.  Since  the 
processes  of  digestion  and  the  main  constituents  of  food 
are  the  same  for  man  as  for  domestic  animals,  no  distinction 
will  be  made  in  this  chapter,  all  the  material  considered 
being  called  food. 

The  tissues  of  the  animal  body  are  in  a  constant  state  of 
change,  new  tissue  being  formed,  old  tissue  being  broken 
down.  These  chemical  processes  of  building  up  and  tearing 
down  are  called  metabolism.  Food  supplies  the  material 
for  constructive  metabolism — anabolism.  For  the  chemical 
changes  of  metabolism  in  general,  for  the  production  of 
heat  and  work  in  the  animal,  energy  is  necessary.  Food 
supplies  the  necessary  material  for  this  energy,  which  is  a 
result  of  destructive  metabolism — katabolism.  A  compara- 
tively small  part  of  the  food  required  for  animals  is  neces- 
(304) 


DIGESTION  305 

sary  in  repairing  and  building  tissue,  the  greater  portion  of 
the  food  being  utilized  in  the  production  of  energy. 

221.  Food  Constituents. — Food  in  general  is  composed  of 
different  kinds  of  material,  every  one  of  which  is  separately 
digested  and  absorbed  in  the  animal  and  which  serves 
special  functions  in  the  body.  These  constituents  are: 
Carbohydrates,  fats,  proteins,  and  inorganic  salts,  not  to 
mention  water  which,  strictly  speaking,  should  be  consid- 
ered a  food  constituent;  but  since  it  is  mixed  with  all  food 
constituents  and  since  its  presence  is  necessary  for  their 
solution  and  absorption,  it  will  not  be  necessary  to  consider 
it  separately. 

222.  Digestion. — The  processes  by  which  insoluble  food 
materials  are  rendered  soluble  for  absorption  into  the  blood 
of  animals  are  called  digestion.  Digestion  takes  place  in  the 
various  parts  of  the  alimentary  canal,  which  consists  prin- 
cipally of  the  mouth,  stomach,  and  small  intestine.  There 
are  connected  with  these  various  parts  of  the  alimentary 
canal  certain  appendages,  which  are  necessary  for  the  various 
activities  (|f  the  food  canal.  Since  digestion  occurs  in  three 
places  and  under  three  different  kinds  of  conditions,  it  is  ad- 
visable to  separate  the  discussion  of  these  processes  into  three 
parts:  Salivary,  gastric,  and  intestinal  digestion. 

(a)  Salivary  Digestion. — The  first  process  is  one  of  masti- 
cation, which  serves  to  grind  the  solid  food  into  more  or  less 
fine  particles  so  that  the  digestive  juices  can  act  on  them  to 
better  advantage.  While  the  food  is  being  masticated,  there 
is  poured  into  the  mouth  from  three  different  pairs  of  glands 
a  liquid  called  saliva,  which  serves  mechanically  to  combine 
the  fine  particles  of  food  together  so  that  they  may  be  more 
easily  swallowed,  and  also  to  act  chemically  on  some  of  the 
food  constituents.  Saliva  is  a  slightly  turbid,  opalescent, 
somewhat  viscid  liquid  which  is  composed  almost  entirely 
of  water,  but  with  some  soluble  organic  matter,  inorganic 
salts,  and  an  enzyme  called  ytyalin.  It  is  slightly  alkaline 
in  character,  due  to  the  presence  of  sodium  carbonate.  The 
enzyme  ptyalin  or  salivary  amylase  is  the  active  digestive 
agent  in  the  mouth.  It  acts  on  starch,  changing  it  first  to 
dextrins  and  then  to  maltose.  The  process  is  hydrolytic  in 
20 


306  FOOD  AND  DIGESTION 

character  and  in  every  way  is  similar  to  the  amylolytic 
action  of  diastase  in  seeds.  The  slightly  alkaline  character 
of  saliva  is  necessary  for  the  activity  of  ptyalin.  It  does  not 
function  in  strong  alkalies  or  acids.  No  other  constituents 
are  acted  upon  in  the  mouth  and  not  all  of  the  starch  is 
rendered  soluble.  Food  material,  now  united  into  a  moist 
ball,  is  swallowed  and  passes  into  the  stomach  where  the 
next  change  takes  place. 

(b)  Gastric  Digestion. — In  man,  horses,  and  pigs,  there  is 
but  one  stomach,  but  in  the  ruminants,  like  cattle  and  sheep, 
there  are  four  stomachs,  or  at  least  four  compartments  to  the 
stomach.  Animals  of  this  type  "chew  the  cud,"  and  food 
passes  from  the  mouth  to  the  first  and  second  compartments 
of  the  stomach,  is  then  forced  back  into  the  mouth  for  further 
mastication,  and  then  after  swallowing  is  passed  finally 
through  the  third  stomach  into  the  fourth  for  final  digestion. 
The  repeated  mastication  of  food  by  these  animals  merely 
serves  to  completely  comminute  the  food  and  thoroughly 
prepare  it  for  digestion.  In  this  way  such  animals  are  able 
to  digest  fibrous  material  to  a  much  greater  extent  than 
other  animals,  like  the  horse.  They  can  digest  more  crude 
fiber  and  cellulose  in  this  way  because  these  insoluble  food 
constituents  are  so.  thoroughl}^  separated  and  ground  up 
that  bacteria  and  possibly  the  digestive  juices  can  act  on 
them  successfully.  In  the  following  discussion  of  gastric 
digestion,  it  will  be  understood  that  the  processes  described 
apply  in  the  case  of  ruminants  to  the  fourth  stomach  only. 

After  the  food  reaches  the  stomach  it  is  mixed  with  the 
gastric  juice,  which  is  secreted  by  glands  in  the  walls  of  the 
stomach  and  is  poured  out  when  the  food  reaches  the  stomach. 
The  process  of  excretion  of  gastric  juice  is  partly  one  of 
response  to  a  mechanical  stimulus  due  to  the  contact  of 
food  with  the  stomach;  partly  to  psychic  impulse  caused  by 
the  sight  or  odor  of  food;  and  partly  in  response  to  nerve 
impulses  when  food  is  masticated.  The  gastric  juice  is 
thoroughly  incorporated  with  the  food  by  to  and  fro  move- 
ments of  the  stomach.  Gastric  juice  is  a  clear,  colorless 
liquid  with  a  distinctly  acid  reaction,  due  to  the  presence  of 
about  0.2  per  cent,  hydrochloric  acid.    It  consists  largely  of 


DIGESTION  307 

water  with  a  little  organic  matter  and  mineral  salts  besides 
the  hydrochloric  acid  just  mentioned.  In  addition  there 
are  present  two  enzymes:  Pepsin  and  rennin.  When  the 
food  first  enters  the  stomach  it  is  alkaline  in  character  due 
to  the  admixture  of  saliva.  The  action  of  ptyalin  continues 
as  long  as  the  reaction  is  alkaline.  As  soon  as  the  food 
becomes  thoroughly  mixed  with  the  acid  gastric  juice  the 
action  of  ptyalin  ceases. 

The  enzyme  pepsin,  for  the  action  of  which  the  acid  solution 
is  necessary,  hydrolyzes  proteins  to  proteoses  and  peptones 
which  are  soluble  decomposition  products  of  proteins.  Not 
all  of  the  proteins  are  acted  upon  in  this  way,  for  the  food 
does  not  remain  in  the  stomach  long  enough  for  the  com- 
plete solution  of  all  proteins  to  take  place.  This  solvent 
action  of  pepsin  is  also  of  secondary  importance  in  that  it 
dissolves  the  protein  cell  walls  of  fats,  thus  disintegrating 
fatty  material  and  setting  free  the  drops  of  fat. 

Rennin,  the  other  enzyme  in  the  stomach,  acts  on  the 
caseinogen  of  milk  (Section  228,  c),  which  is  a  soluble  com- 
pound, changing  it  or  "curdling"  it  to  a  solid  compound, 
casein.  Just  why  this  is  necessary  is  not  apparent.  After 
the  change  takes  place  the  coagulated  casein  is  dissolved  by 
the  pepsin.  No  other  food  constituents  are  acted  upon  in 
the  stomach.  There  is  no  evidence  that  the  hydrochloric 
acid  inverts  sucrose,  as  might  be  expected  (Section  5). 
The  combined  action  of  water,  hydrochloric  acid,  and  pepsin, 
together  with  the  mixing  and  churning  motions  of  the 
stomach  has  now  changed  the  solid  elements  of  food  material 
to  a  semi-liquid  form  called  chyme. 

(c)  Intestinal  Digestion. — ^The  chyme  is  discharged  into 
the  small  intestine  where  the  next  processes  of  digestion 
take  place.  The  food  material  here  is  mixed  with  three 
different  fluids,  intestinal  juice,  pancreatic  juice,  and  bile. 

Intestinal  juice  is  secreted  by  certain  glands  in  the  walls 
of  the  small  intestine  and  is  a  watery,  light  yellow,  slightly 
opalescent,  alkaline  liquid,  containing  at  least  carbonates. 
Because  it  is  very  difficult  to  obtain  it  in  the  pure  state,  its 
composition  is  not  accurately  known  except  that  it  does 
contain  certain  enzymes  which  are  active  in  hydrolyzing 


308  FOOD  AND  DIGESTION 

some  of  the  carbohydrates.  Invertase  changes  sucrose  to 
dextrose  and  levulose;  maltose  changes  maltose  to  dextrose; 
and  lactase  changes  lactose  to  dextrose  and  galactose. 

Pancreatic  juice  is  secreted  by  the  pancreas,  which  is  a 
long  flattened  gland,  and  is  discharged  into  the  intestine 
like  the  intestinal  juice  when  food  reaches  the  stomach. 
Pancreatic  juice  is  a  clear,  viscid,  decidedly  alkaline  liquid, 
containing  in  addition  to  water  a  little  organic  matter  and 
inorganic  salts  of  which  sodium  carbonate  is  the  most 
important  and  which  gives  alkalinity  to  the  juice.  Pan- 
creatic juice  contains  the  principal  digestive  enzymes  of  the 
alimentary  canal. 

Amyloysin  is  the  pancreatic  amylase  which  hydrolyzes 
starch  to  maltose,  being  much  more  energetic  in  action  than 
ptyalin.    An  alkaline  solution  is  necessary  for  it  to  act. 

Steapsin  is  the  pancreatic  lipase  which  hydrolyzes  fat 
to  glycerine  and  fatty  acids.  The  fatty  acids  thus  liberated 
unite  with  the  alkalies  which  are  present  in  the  juice  of  the 
intestine  to  form  soaps.  It  is  not  definitely  known  whether 
all  fats  are  thus  hydrolyzed  or  whether  a  part  of  the  fat  is 
so  changed  and  the  remainder  emulsified  in  the  soap  solution. 
The  former  is  the  more  probable,  however.  This  enzyme 
also  is  only  active  in  an  alkaline  solution. 

Trypsin  is  the  pancreatic  protease  which  hydrolyzes 
proteins  in  the  alkaline  medium  and  changes  them  to  pep- 
tones and  usually  to  amino-acids.  Trypsin  is  much  more 
energetic  in  its  action  than  is  pepsin  in  the  stomach  and  the 
probabilities  are  that  it  hydrolyzes  the  proteins  more  com- 
pletely. 

Bile  is  a  fluid  secreted  by  the  liver  and  discharged  into 
the  small  intestine  together  with  intestinal  juice  and  pan- 
creatic juice  when  food  is  received  into  the  stomach.  It  is 
a  thin  liquid  somewhat  viscid,  of  bitter  taste,  and  very 
alkaline  due  to  the  presence  of  sodium  carbonate  and  sodium 
phosphate.  It  varies  in  color  from  greenish  yellow  to 
brownish  red,  depending  on  the  animal.  In  herbivorous,  or 
plant-eating  animals,  it  is  greenish  in  color;  in  carnivorous, 
or  meat-eating  animals,  it  is  orange  or  brown.  There  are 
present  in  the  bile  in   addition  to  the  normal   secretory 


ABSORPTION  OF  FOOD  CONSTITUENTS  309 

compounds  some  excretory  or  waste  compounds  such  as 
cholesterin  and  lecithin.  They  are  supposed  to  be  decom- 
position products  of  the  nerve  tissue  and  are  eHminated 
from  the  blood  stream  through  the  liver.  The  bile  has  no 
direct  solvent  action  on  any  of  the  food  constituents,  but 
its  action  decidedly  increases  the  power  of  the  pancreatic 
enzymes  and  it  serves  as  the  principal  solvent  for  the  fatty 
acids  in  the  formation  of  soaps. 

In  addition  to  the  normal  enzyme  secretions  of  the  body 
which  have  a  solvent  action  on  food  constituents,  there  are 
ordinarily  present  in  animals  large  numbers  of  bacteria, 
principally  in  the  intestines.  Their  presence  is  not  necessary 
for  the  decomposition  and  solution  of  food  constituents, 
but  it  is  probable  that  their  fermentative  action  is  in  some 
cases  of  benefit  in  digesting  food. 

Food  material  w^hich  has  been  acted  upon  by  the  various 
chemical  agents  is  rendered  soluble  and  ready  for  ab- 
sorption. Not  all  of  it,  however,  can  be  dissolved.  Par- 
ticularly do  crude  fiber  and  cellulose  remain  unattacked 
except  in  the  case  of  some  of  the  domestic  animals,  more 
particularly  the  ruminants,  where  these  food  constituents 
are  partly  digested,  due  probably  to  the  activity  of  bacteria. 
The  undigested  portion  of  the  food  is  discharged  into  the 
large  intestine  for  final  elimination. 

223.  Absorption  of  Food  Constituents. — The  absorption  of 
the  various  constituents  of  the  food  is  limited  almost  wholly 
to  the  small  intestine,  little  if  any  being  absorbed  from  the 
mouth  or  stomach  into  the  circulatory  system.  The  interior 
of  the  small  intestine  is  covered  with  minute  conical  projec- 
tions called  villi  (Fig.  81),  through  which  all  the  dissolved 
material  is  absorbed.  They  serve  the  same  purpose  in  the 
animal  that  the  root  hairs  do  in  the  plant,  but  they  differ 
in  that  they  are  not  each  one  a  single  cell  but  a  large  number 
of  cells  containing  blood  capillaries  and  lymph  vessels,  which 
carry  the  absorbed  material  into  the  general  circulatory 
system. 

The  carbohydrates  in  the  form  of  dextrose,  levulose,  and 
possibly  galactose  are  absorbed  through  the  outer  cells  of  the 
villi  into  the  capillaries,  which  finally  unite  into  the  portal 


310 


FOOD  AND  DIGESTION 


vein  and  discharge  into  the  Hver.  In  the  Hver  the  carbo- 
hydrates are  changed  into  glycogen  until  such  time  as 
dextrose  is  needed  in  the  blood,  when  the  glycogen  is  trans- 
formed into  dextrose.  Enzymes  in  the  liver  accomplish  the 
dehydration  change  to  glj^ogen  as  well  as  the  hydrolytic 
change  to  dextrose. 


Vein 


Artery 


Central  lacteal 


m^s^i^it^^fB^iii?^ 


Fig.  81. — Diagrammatic  section  through  villi  of  small  intestine. 
Bohm  and  Davidoff,  after  Mall.) 


(From 


Fats  are  probably  absorbed  as  glycerine  and  soaps, 
although  possibly  also  in  the  form  of  emulsified  fats,  and  pass 
through  these  outer  cells  of  the  villi  into  the  lymph  vessels  or 
lacteals.  During  the  process  of  this  absorption  the  glycerine 
unites  with  the  fatty  acids  of  the  soaps  to  form  fats,  so  that 
the  lymph  as  it  leaves  the  villi  is  charged  with  liquid  globules 
of  fat  to  such  an  extent  as  to  give  it  the  appearance  of  milk. 
The  lymph  vessels  join  the  thoracic  duct  from  which  the 
fatty  particles  are  discharged  into  the  veins  and  thus  get 
into  the  general  circulatory  system  of  the  blood. 

The  proteins  chiefly  in  the  form  of  amino -acids  are 
absorbed  into  the  blood-vessels  of  the  villi,  during  which 
process  they  combine  to  form  the  serum-albumin  and  globulin 


FUNCTIONS  OF  FOOD  CONSTITUENTS  311 

of  the  blood.  These  are  the  forms  of  protein  which  are  trans- 
ported through  the  body.  The  proteins  pass  into  the  portal 
vein  and  through  the  liver,  but  are  not  arrested  there  as  are 
the  carbohydrates,  unless  in  excess  when  they  are  changed 
to  carbohydrate  and  urea. 

Water  and  inorganic  salts  which  have  been  set  free  from 
their  organic  combination  in  foods  by  the  various  processes 
of  digestion  are  absorbed  through  the  villi  into  the  capillaries. 
Under  ordinary  conditions  no  water  is  absorbed  by  the 
lymph  vessels.  The  progress  of  water  and  inorganic  salts 
is  then  like  that  of  carbohydrates  and  proteins,  through  the 
portal  vein  and  the  liver.  Fig.  82  shows  the  routes  of  the 
absorbed  material. 

224.  Functions  of  Food  Constituents. — Various  constituents 
of  the  food  after  absorption  into  the  body,  serve  each  a  more 
or  less  distinct  function  in  the  activity  of  the  animal  and 
can  be  discussed  separately. 

(a)  Carbohydrate. — ^The  only  active  form  of  carbohy- 
drate in  the  body  is  dextrose  and  this  material  serves  primarily 
as  a  source  of  energy.  Just  as  energy  is  derived  in  the  steam 
engine  from  the  combustion  of  fuel  so  is  the  energy  of  the 
body  derived  from  combustion  of  fuel.  This  combustion 
takes  place  within  the  tissues  of  the  body  and  is  caused 
by  enzymes,  the  final  product  being  carbon  dioxide  and 
water.  Energy  is  set  free  in  the  form  of  heat  and  work. 
When  dextrose  is  present  in  larger  quantities  than  is  necessary 
for  fuel  consumption  it  is  transformed  into  fat  and  stored 
away  in  the  adipose  tissue  of  the  body. 

(6)  Fat  serves  also  as  fuel  for  body  energy  and  is 
the  most  concentrated  source  of  fuel  in  the  body,  yielding 
more  energy  per  unit  of  weight  than  any  other  form  of  fuel. 
Some  of  the  fat  absorbed  is  deposited  in  adipose  tissue,  and 
there  is  some  evidence  that  dextrose  may  be  formed  from  fat. 

(c)  Protein. — ^The  primary  function  of  protein  is,  of 
course,  to  supply  the  principal  part  of  tissue  material.  It  is 
necessary  for  cell  walls  and  protoplasmic  contents  of  new 
cells  and  also  to  replace  worn  out  material  in  old  cells. 
Changes  are  constantly  taking  place  in  the  body;  old  cells 
wearing  out,  new  cells  being  formed,  in  addition  to  increase 
in  the  number  of  cells  when  an  animal  is  growing.     Protein 


Fig.  82. — Diagram  showing  the  routes  by  which  the  absorbed  foods  reach 
the  blood  of  the  general  circulation.  (G.  Bachman.)  I.  i.,  loop  of  small 
intestine;  int.  v.,  intestinal  veins  converging  to  form  in  part,  p.  v.,  the  portal 
vein,  which  enters  the  liver  and  by  repeated  branchings  assists  in  the  forma- 
tion of  the  hepatic  capillary  plexus;  h.  v.,  the  hepatic  veins  carrying  blood 
from  the  liver  and  discharging  it  into,  inf.  v.  c,  the  inferior  vena  cava; 
int.  I.  v.,  the  intestinal  lymph  vessels  converging  to  discharge  their  contents, 
chyle,  into,  rec.  c,  the  receptacuium  chyli,  the  lower  expanded  part  of  the 
thoracic  duct;  th.  d.,  the  thoracic  duct  discharging  lymph  and  chyle  into  the 
blood  at  the  junction  of  the  internal  jugular  and  subclavian  veins;  sup.  v.  c, 
the  superior  vena  cava. — Brubaker's  Physiology. 


HOW  TO  EXPRESS  FOOD  VALUE  313 

also  serves  as  a  source  of  fuel  in  the  body,  particularly  when 
dextrose  and  fat  are  not  present  in  sufficient  amount. 
The  products  of  protein  oxidation,  however,  in  addition  to 
carbon  dioxide  and  water,  are  nitrogenous  compounds, 
largely  urea.  The  protein  compounds  can  also  be  split 
up  in  the  body  into  a  nitrogenous  and  a  non-nitrogenous 
residue.  From  the  non-nitrogenous  residue  carbohydrates 
can  be  formed  and  there  is  some  evidence  to  show  that  fat 
may  also  be  formed.  The  nitrogenous  residue  is  eliminated 
as  waste  material. 

(d)  Inorganic  Elements. — These  constituents  in  mineral 
form  give  rigidity  to  the  skeleton.  They  serve  also  as  neces- 
sary constituents  of  protoplasm,  sulphur  and  phosphorus,  for 
example,  and  are  combined  organically  for  this  purpose. 
Finally,  these  elements  in  the  form  of  inorganic  salts  are 
present  in  the  fluids  and  tissues  of  the  body,  having  an 
influence  upon  the  activities  of  the  muscles  and  nerves, 
supplying  an  alkaline  or  acid  reaction  as  may  be  necessary, 
and  regulating  the  osmotic  pressure  of  the  cells. 

225.  How  to  Express  Food  Value. — As  has  been  stated 
(Section  222,  c),  not  all  of  the  food  taken  in  by  the  animal  is 
absorbed,  and  of  course,  that  portion  which  is  not  digested  is 
of  no  use  to  the  animal.  It  is  customary  to  express  the 
amount  of  digestible  material  in  each  constituent  in  per- 
centage. These  "digestible  coefficients,"  as  they  are  called, 
are  determined  by  analyzing  the  original  food  and  also  by 
analyzing  all  excreted  waste  products.  The  difference 
between  the  two  sets  of  results  gives  the  percentage  of  food 
digested,  and  hence  serves  as  an  indication  of  the  amount 
of  tissue  building  or  energy  material  in  the  food  eaten. 
The  results,  however,  are  not  absolutely  correct  for  several 
reasons.  In  the  first  place  the  excreted  material  contains 
protein  and  ether  soluble  material  called  fat,  derived  from 
the  intestinal  juices  and  waste  cells  of  the  intestines. 
In  the  second  place,  unless  there  is  an  analysis  of  all  the 
gas  eliminated  from  the  body  there  is  a  waste  of  some 
material  in  this  way  that  is  unaccounted  for.  In  the  third 
place,  if  it  is  desired  to  determine  the  value  of  the  food  for 
the  production  of  work  or  milk  or  fat,  it  is  necessary  to 


314  FOOD  AND  DIGESTION 

take  into  consideration  the  food  constituents  which  are 
consumed  by  the  involuntary  activities  of  the  body.  An 
animal  absolutely  at  rest  or  asleep  is  constantly  using  up 
food  constituents.  The  beating  of  the  heart,  expansion  and 
contraction  of  the  lungs,  movements  of  the  digestive  ap- 
paratus are  going  on  constantly.  When  food  is  masticated 
work  is  done  and  the  oxidation  of  body  fuel  is  necessary  to 
obtain  this  energy. 

Most  of  the  food  taken  in  by  the  animal  is  used  up  in  the 
production  of  energy,  and  since  energy  can  be  expressed  in 
terms  of  heat,  it  is  customary  to  value  food  on  the  basis  of 
heat  equivalents.  Since  the  combustion  of  food  material 
in  the  body  results  in  the  production  of  exactly  as  much 
heat  as  is  derived  from  the  combustion  of  the  same  con- 
stituents in  the  air,  it  is  possible  to  determine  the  fuel  value 
of  foods  by  well  known  methods  of  analysis.  And,  finally, 
since  an  apparatus  has  been  devised  for  determining  the 
energy  value  of  foods  in  the  animal,  and  at  the  same  time 
permitting  a  complete  analysis  of  all  food  income  and  outgo, 
it  is  possible  to  overcome  in  large  measure  the  defects  just 
mentioned  for  determining  the  value  of  foods. 

For  the  determination  of  the  heat  value  of  substances, 
an  instrument  called  a  calorimeter  is  used,  which  consists 
essentially  of  a  closed  chamber  in  which  organic  material 
can  be  burned  in  an  atmosphere  of  oxygen  and  the  resulting 
heat  accurately  measured  by  the  rise  in  temperature  of  a 
surrounding  body  of  water  after  making  certain  necessary 
corrections.  Modern  scientific  ingenuity  has  gone  one  step 
further  and  devised  calorimeters  which  will  contain  a 
living  animal  and  in  this  way  the  amount  of  heat  developed 
by  the  combustion  of  food  in  the  body  can  be  accurately 
measured.  In  addition  these  animal  calorimeters  are 
equipped  with  elaborate  apparatus  for  measuring  the  intake 
of  oxygen  and  the  output  of  carbon  dioxide  and  other  gases. 
These  factors,  together  with  the  weighing  and  analyzing 
of  all  foods  consumed  and  all  solid  and  liquid  material 
excreted,  make  it  possible  by  a  series  of  calculations  to 
arrive  very  accurately  at  the  proper  value  of  any  food  for 
any  particular  animal.    The  respiration  calorimeter  devised 


HOW  TO  EXPRESS  FOOD    VALUE 


315 


by  Armsby  of  the  Pennsylvania  Station  is  the  most  complete 
apparatus  of  this  kind  in  existence.  Fig.  83  shows  the 
apparatus  from  the  outside. 


316  FOOD  AND  DIGESTION 

The  unit  for  expressing  food  values  in  terms  of  heat  is 
the  large  Calorie  which  is  the  amount  of  heat  necessary  to 
raise  the  temperature  of  1000  grams  of  water  1°  C.  For  many 
purposes,  however,  this  unit  is  not  large  enough  for  con- 
venience and  as  a  result  the  unit  therm  is  now  in  use  by 
Armsby.  A  therm  is  the  quantity  of  heat  necessary  to  raise 
the  temperature  of  1000  kilograms  of  water  1°  C,  and  it  is 
customary  in  expressing  the  value  of  food  to  do  so  as  therms 
per  100  pounds. 

226.  Feeding  Standards. — Ever  since  the  functions  of  the 
various  food  constituents  in  animal  metabolism  have  been 
known  there  has  been  a  desire  to  determine  scientifically  the 
amount  of  these  constituents  necessary  for  various  classes 
of  animals  and  for  various  purposes.  As  a  result  we  have 
the  so-called  "feeding  standards,"  which  are  based  on 
analytical  and  experimental  data.  The  accurate  obser- 
vations of  Armsby  with  his  respiration  calorimeter  now  make 
it  possible  to  establish  standards  which  are  reasonably 
correct.  Although  even  so,  our  knowledge  is  not  by  any 
means  perfect.  The  question  of  the  proper  feeding  of  stock, 
and  what  should  be  more  important  the  proper  feeding  of 
man,  is  too  large  a  one  to  be  considered  here.  For  further 
information  along  this  line  the  reader  is  directed  to  the 
references  given  at  the  end  of  the  chapter. 

EXERCISES 

1.  Does  the  action  of  ptyalin  form  diffusible  products  from  starch?  If 
not,  what  enzyme  does  do  so?  Where  is  each  secreted?  What  kind  of  a 
medium  is  required  by  each?  When  will  ptyalin  stop  acting  and  when 
will  the  other  enzyme  begin  acting? 

2.  What  causes  an  animal's  mouth  to  water?  Of  what  value  is  this 
phenomenon? 

3.  Is  hydrolysis  of  fat  sufficient  to  make  diffusible  products?  Why  or 
why  not? 

4.  Why  is  it  wise  to  chew  food? 

5.  Can  you  suggest  whether  or  not  drinking  water  at  meal  time  is  a  good 
practice? 

6.  What  are  the  three  functions  of  bile? 

7.  What  happens  to  each  of  the  six  groups  of  the  Weende  method  (Chap. 
IV)  in  the  passage  of  food  through  the  digestive  tract? 

9.  What  is  the  function  of  digestion? 


REFERENCES 


317 


REFERENCES 

Armsby.     Principles  of  Animal  Nutrition  and  The  Nutrition  of  Farm 
Animals. 

Brubaker.     Text  Book  of  Physiology. 

Halligan.     Elementary  Treatise  on  Stock  Feeds  and  Feeding. 

Henry.     Feeds  and  Feeding. 

Jordan.     The  Feeding  of  Animals. 

McCoUuni:     The  Newer  Knowledge  of  Nutrition. 

Sherman.     Chemistry  of  Food  and  Nutrition. 

Smith.     Manual  of  Veterinary  Physiology. 

Starling.     Human  Physiology. 


CHAPTER  XIX 

MILK  AND  DAIRY  PRODUCTS 

The  most  valuable  products  of  the  animal  are  milk  and  its 
derivatives.  Most  of  these  materials  are  used  as  food  for 
man.  Milk  in  particular,  as  Hawk  says,  is  the  most  satis- 
factory individual  food  material  elaborated  by  nature,  in 
that  it  contains  protein,  fat,  and  carbohydrate  in  addition 
to  mineral  matter,  all  combined  in  such  form  and  proportion 
as  to  make  it  palatable,  nourishing,  and  easily  digested. 
The  following  discussion  applies  solely  to  milk  from  cows, 
since  that  has  been  most  studied  and  since  milk  from  other 
animals  differs  from  it  only  in  the  proportion  of  the  various 
constituents. 

227.  Physical  Appearance. — Milk  is  a  white,  opaque 
liquid,  the  specific  gravity  of  which  is  about  1.03,  with  a 
slightly  sweet,  pleasing  taste,  and  a  freezing  point  of  —0.56°  C. 
Its  color  is  due  to  minute  particles  of  fat  in  suspension  and 
also  to  the  presence  of  a  protein,  caseinogen,  in  pseudo- 
solution. 

228.  Chemical  Composition. — Milk  is  composed  of  a  clear, 
aqueous  solution  of  carbohydrate,  inorganic  salts,  and 
protein,  in  which  are  suspended  fat  globules,  calcium  phos- 
phate, and  a  protein  in  semi-suspension.  The  average  com- 
position is  as  follows:  Water,  87.75  per  cent.;  fat,  3.4  per 
cent.;  protein,  3.5  per  cent.;  carbohydrate,  4.6  per  cent.; 
and  inorganic  salts,  0.75  per  cent. 

(a)  Carbohydrate. — Lactose  is  the  only  carbohydrate 
present  in  milk  sugar.  It  is  an  aldose  sugar  whose  formula  is 
C12H22O11,  graphically: 


CHEMICAL  COMPOSITION  319 


H— C— O— H 

I 
H— C— O— H 


It  is  dextrorotatory  and  reduces  Fehling's  solution,  although 
to  a  less  extent  than  dextrose.  It  is  hydrolyzed  by  enzjines 
and  acids  to  dextrose  and  galactose.  It  does  not  undergo 
ordinary  alcoholic  fermentation  except  under  the  influence 
of  certain  yeasts.  The  principal  change  in  lactose  is  due 
to  the  so-called  lactic  bacteria  which  hydrolyze  it  to  lactic 
acid,  thus : 

C12H22O11  +  H2O  =  4C8H6O3. 

It  is  this  lactic  acid  to  which  is  due  the  taste  of  sour  milk, 
and  it  is  produced  so  quickly  that  ordinary  milk  contains 
about  0.2  per  cent,  of  lactic  acid.  The  taste  is  apparent 
when  the  proportion  rises  to  0.4  per  cent.,  and  at  0.7  per  cent, 
milk  "curdles."  Curdling  is  due  to  the  coagulation  of  case- 
inogen  (see  below).  The  percentage  of  lactic  acid  rarely 
rises  above  2  because  in  that  amount  the  action  of  the 
lactic  acid  bacteria  is  inhibited.  Lactose  is  only  one-tenth 
as  sweet  as  sucrose. 

(6)  Fat  in  milk  is,  of  course,  like  other  fixed  oils 
in  that  it  is  composed  of  glycerides  of  fatty  acids.  Milk 
fat  differs  from  other  animal  fat  in  that  it  contains  the  gly- 
ceride  of  a  number  of  lower  fatty  acids,  there  having  been 
found  the  following: 


320  MILK  AND  DAIRY  PRODUCTS 

Butyric,    C3H7COOH 

Caproic,   CsHuCOOH 

Caprylic,  CrHiaCOOH 

Capric,     C,Hi,COOH 

Laurie,     CnH23COOH 

Myristic,  C13H27COOH 

Palmitic,  C15H31COOH 

Stearic,     C17H35COOH 

Oleic,        C17H33COOH 

Dihydroxystearic,  Ci7H33(OH)2COOH 

In  general,  oleic  and  palmitic  acids  are  present  to  the  greatest 
extent.  The  fats  from  butyric,  caproic,  caprylic,  and  oleic 
acids  are  liquid.  The  fats  from  the  other  acids  are  solid. 
The  first  four  mentioned  fatty  acids  are  soluble  in  water 
and  volatile  in  steam.  All  the  acids  are  saturated  with  the 
exception  of  oleic.  Milk  fat  is  soluble  in  the  usual  solvents : 
Ether,  carbon  disulphide,  acetone,  and  liquid  hydrocarbons. 

Milk  fat  occurs  in  small  globules  from  1.6  to  10  microns 
in  diameter  (0.0016  to  0.01  mm.).  They  are  liquid  in  the 
animal,  but  solid  at  ordinary  temperatures,  the  melting 
point  varying  from  29.5°  to  33°  C.  The  fat  globules  in  milk 
are  in  the  form  of  a  true  emulsion — minute,  oily  particles 
suspended  in  a  slightly  viscous  medium  (Section  204,  II,  b), 
the  viscosity  of  the  milk  plasma  being  due  to  the  soluble 
proteins.  Referring  to  the  specific  gravity  of  milk,  it  may 
be  noted  that  an  increase  in  the  amount  of  fat  causes  a 
lowering  of  the  specific  gravity.     ^ 

(c)  Proteins  consist  of  caseinogen,  lactalbumin,  and  one 
or  two  others  not  of  sufficient  importance  to  deserve 
mention.  Caseinogen  helps  to  give  the  opaque  color  to 
milk,  being  present  in  a  condition  of  pseudosolution.  It 
contains  sulphur  and  phosphorus  in  addition  to  the  ordinary 
protein  elements,  carbon,  hydrogen,  nitrogen,  and  oxygen, 
and  is  probably  combined  with  calcium  or  with  calcium 
phosphate.  Acids  precipitate  the  casein  by  removing  the 
calcium,  thus  setting  free  the  protein  proper.  The  action  of 
rennin  in  precipitating  casein  is  somewhat  different.  It  splits 
the  caseinogen  into  two  different  soluble  proteins,  at  the 


SECRETION  321 

same  time  liberating  the  calcium  phosphate.  One  of  the 
proteins  unites  with  the  liberated  calcium  phosphate  to  form 
the  insoluble  curd.  Casein  is  insoluble  in  water,  alcohol, 
ether,  and  dilute  acids,  but  soluble  in  strong  acids  and  in 
alkalies. 

Lactalbumin  is  coagulated  by  heat  and  precipitated  by 
tannin  and  saturated  solutions  of  sodium  and  magnesium 
sulphates.  It  contains  carbon,  hydrogen,  oxygen,  nitrogen, 
and  sulphur,  but  no  phosphorus. 

(d)  Inorganic  Salts  are  present  in  the  form  of  chlorides 
of  sodium  and  potassium,  mono-  and  dipotassium  phos- 
phates, dimagnesium  phosphate,  di-  and  tricalcium  phos- 
phates, calcium  and  magnesium  citrates.  All  the  salts 
are  present  in  solution  except  tricalcium  phosphate,  which 
is  suspended  in  finely  divided  form.  It  is  to  be  noted  that 
some  of  the  inorganic  elements  are  combined  with  citric  acid. 
It  may  be  noted  that  an  increase  in  the  amount  of  inorganic 
salts  raises  the  specific  gravity. 

(e)  Other  Constituents. — In  addition  to  those  substances 
already  mentioned,  milk  contains  lecithin,  cholesterol,  pro- 
teolytic enzymes,  carbon  dioxide,  oxygen  and  other  gases, 
especially  when  the  milk  is  fresh  drawn,  not  to  mention 
various  kinds  of  foreign  matter  including  bacteria.  The 
amount  of  dirt  and  bacteria  depends  on  the  care  with  which 
milk  is  handled. 

229.  Secretion. — Milk  is  secreted  in  certain  glands  espe- 
cially adapted  for  the  purpose,  and  evidence  points  to  the 
fact  that  the  various  components  of  this  fluid  are  elaborated 
in  these  gland  cells  only  and  not  merely  filtered  from  the 
blood  plasma.  Lactose,  for  example,  is  not  found  in  the 
blood  stream,  but  must  be  manufactured,  probably  from 
dextrose,  in  the  milk  glands.  Milk  fat  and  casein  are  not 
found  in  any  other  part  of  the  body. 

The  influence  of  breed  of  cow  on  the  quality  of  milk 
secretion  is  of  much  greater  importance  than  that  of  food. 
The  Jersey,  for  example,  produces  large  globules  of  milk 
fat,  which  causes  cream  to  rise  rapidly  and  in  considerable 
quantities.  The  Holstein  produces  small  globules  of  milk 
fat  and  not  so  great  a  total  quantity.  Modifying  the  food 
21 


322  MILK  AND  DAIRY  PRODUCTS 

has  very  little  influence  on  the  composition  of  milk.  The 
same  food,  for  example,  fed  to  different  breeds  produces 
different  kinds  of  milk,  but  changing  the  food  for  one  par- 
ticular breed  does  not  change  the  kind  of  milk  produced 
by  that  breed.  There  are  some  exceptions  to  this  statement, 
but  they  are  not  of  sufficient  importance  to  be  discussed 
here. 

230.  Adulteration  and  Preservation. — Since  milk  has  be- 
come such  a  very  valuable  food  product,  the  temptation 
to  adulterate  it  is  very  great.  The  addition  of  water  is  the 
commonest  method  of  adulteration,  detection  of  which  is 
not  particularly  easy.  For  example,  the  specific  gravity  of 
milk  might  be  used  as  a  test  for  purity,  but  by  removing 
fat  and  adding  water,  the  specific  gravity  can  be  made  to 
remain  the  same.  It  is,  however,  a  requirenient  in  some 
states  that  milk  shall  not  be  sold  under  a  certain  content  of 
butter  fat.  This  serves  as  a  protection  to  the  consumer, 
but  in  some  instances  it  works  a  hardship  against  the  pro- 
ducer for  it  is  quite  possible  that  perfectly  pure  milk  may 
contain  less  than  the  stated  legal  minimum  amount  of  fat. 

Milk  is  not  only  a  perfect  nutrient  for  man,  but  it  is  also 
a  perfect  nutrient  for  bacteria,  and  exposure  to  the  air  for 
any  length  of  time  permits  the  entrance  of  large  numbers 
of  bacteria,  many  of  them  dangerous  to  health.  No  bacteria 
are  present  in  the  milk  within  the  animal,  but  as  soon  as  it 
is  drawn  bacteria  begin  to  accumulate.  Since  bacteria  thrive 
best  in  warm  milk,  immediate  cooling  helps  to  some  extent  in 
preventing  their  activity. 

There  are  two  ways  of  freeing  milk  from  bacteria,  which 
are  legitimate.  One  is  by  pasteurization  which  consists 
in  heating  the  milk  to  a  temperature  of  60°  to  80°  C.  for 
twenty  minutes,  and  then  cooling  it.  This  treatment  kills 
practically  all  of  the  bacteria,  and  if  carried  out  in  sealed 
containers  no  more  bacteria  can  enter.  Pasteurization  does 
not  alter  the  taste  or  smell  of  the  milk,  and  is  practised 
quite  largely  by  the  best  dairies. 

The  other  way  of  treating  milk  is  by  sterilization  which 
consists  in  heating  the  milk  to  115°  C,  accomplished  by 
steam  under  pressure.     This  absolutely  kills  all  bacteria, 


BUTTER  323 

but  it  alters  the  taste  and  smell  of  the  milk.  Albumin  is 
precipitated,  calcium  citrate  is  deposited,  and  other  changes 
also  take  place  which  affect  the  quality  of  the  milk. 

It  is  unfortunately  easier  to  stop  the  action  of  bacteria 
by  the  addition  of  chemical  preservatives,  and  the  ones  which 
are  most  effective  in  killing  bacteria  are  also  the  ones  which 
harm  the  consumer.  Formaldehyde,  boric  acid,  salicylic 
acid,  and  benzoic  acid,  are  compounds  which  have  been 
used,  but  the  law  in  most  states  prevents  their  use  at  all, 
so  that  at  the  present  time  the  consumer  is  safe  from  such  a 
dangerous  practice. 

231.  Cream. — Cream  consists  merely  of  the  greater  part 
of  the  milk  fat  separated  from  the  remainder  of  the  milk, 
and  is  obtained  by  allowing  the  milk  to  stand  quietly  when 
the  fat  globules,  being  lighter  than  the  rest  of  the  milk,  rise 
to  the  surface  and  can  be  skimmed  off.  Another  way  to 
obtain  cream  is  by  use  of  the  separator,  which  is  a  machine 
where  the  fresh  drawn  milk  can  be  subjected  to  centrifugal 
force,  the  heavier  part  being  thrown  to  the  outside  and  the 
lighter  part  rising  in  the  centre.  By  appropriate  dexices 
the  two  parts  of  the  milk  can  be  drawn  off  in  separate  streams 
and  by  regulating  the  cream  discharge  pipe,  cream  of  difl'erent 
fat  content  can  be  obtained.  The  fat  can  be  withdrawn 
more  completely  from  milk  in  this  way  than  it  can  by  the 
old-fashioned  skimming  process,  the  former  removing  from 
97  to  98  per  cent,  of  the  butter  fat  under  the  best  conditions, 
and  the  latter  not  more  than  90  to  95  per  cent. 

232.  Butter. — Both  butter  and  cream  consist  of  milk  fat, 
but  cream  is  mixed  with  more  or  less  of  the  other  con- 
stituents of  milk,  whereas  butter  consists  practically  of  milk 
fat  only.  It  is  made  by  agitating  cream  in  a  churn  whereby 
the  globules  of  milk  fat  coalesce  into  a  mass.  This  is  removed 
and  worked  over  to  remove  the  last  trace  of  buttermilk,  which 
consists  of  milk  minus  butter.  Buttermilk  usually  contains 
about  4  per  cent,  of  lactic  acid,  giving  it  a  sour  taste.  This 
is  because  the  best  quality  of  butter  is  obtained  from  cream 
which  has  been  properly  "ripened,"  or,  to  put  it  plainly, 
which  is  somewhat  sour.  The  souring,  however,  is  not 
permitted   to   take   place   spontaneously,   because   of   the 


324  MILK  AND  DAIRY  PRODUCTS 

danger  of  introducing  harmful  bacteria,  but  is  accomplished 
by  adding  artificial  lactic  acid  bacteria  cultures.  Butter 
contains  about  84  per  cent,  of  fat,  13  per  cent,  of  water,  and 
about  3  per  cent,  of  lactose,  albumin,  and  sodium  chloride, 
the  latter  having  been  added  to  improve  the  flavor  and  also 
to  serve  as  a  preservative.  Since  it  is  possible  to  produce 
butter  which  contains  considerable  water  and  thus  sell  an 
adulterated  product,  it  is  not  permitted  in  the  United  States 
for  butter  to  contain  more  than  16  per  cent,  of  water. 

Butter  frequently  becomes  rancid,  a  condition  which  is 
due  probably  to  the  action  of  bacteria,  molds,  light,  and  oxy- 
gen. This  combination  -of  factors  results  in  the  hydrolysis 
of  fat,  which  sets  free  some  of  the  fatty  acids,  one  of  them 
at  least,  butyric,  being  volatile,  and  some  of  them  oxidizing 
to  aldehydes. 

Oleomargarine. — ^At  this  point  it  may  be  well  to  mention 
one  of  the  principal  butter  substitutes,  which  is  a  perfectly 
nutritious  article  of  food,  but  which  not  being  butter  should 
not  be  sold  as  such.  It  is  manufactured  from  beef  fat  by 
rendering  the  latter  and  allowing  the  resultant  product  to 
stand  at  a  low  temperature  for  some  time,  when  part  of  the 
solid  fats  crystallize.  The  soft  mass  is  now  subjected  to 
pressure,  and  a  liquid  oil  consisting  of  olein  and  palmitin 
principally  is  pressed  out.  This  "oleo  oil"  is  worked  up 
by  itself  or  with  lard,  cottonseed  oil,  cocoanut  and  other 
oils.  It  is  then  churned  wuth  milk,  sometimes  with  a  little 
butter,  after  which  it  is  worked  and  salted. 

233.  Cheese. — ^This  is  one  of  the  oldest  articles  of  food, 
being  used  1000  years  B.  C,  and  still  retaining  its  popularity 
as  a  nutritious  article  of  diet.  It  consists  essentially  of  the 
casein  from  milk  with  considerable  fat  entangled  with  it 
and  some  water,  lactose,  and  inorganic  salts.  The  solid 
product  is  submitted  to  seasoning  and  ripening  processes 
which  favorably  affect  its  composition  and  flavor.  Ordinary 
American  cheese  contains  about  34.4  per  cent,  water,  26.4 
per  cent,  protein,  32.7  per  cent,  fat,  2.9  per  cent,  lactose, 
and  3.6  per  cent.  ash. 

Cheddar,  or  American  cheese,  is  the  commonest  form  of  this 
food.    It  is  made  by  first  ripening  the  milk  with  an  artificial 


CHEESE  325 

starter  until  it  contains  a  small  amount  of  lactic  acid.  Then 
rennet  is  added.  This  is  a  preparation  made  from  calves' 
stomachs  and  contains  the  enzyme  rennin  which  coagulates 
the  casein  in  the  milk.  The  temperature  is  maintained  at 
about  30°  C.  until  a  curd  settles,  when  it  is  raised  somewhat 
higher  and  maintained  for  one  or  two  hours.  After  separating 
the  curd  from  the  "whey,"  as  the  residual  liquid  is  called, 
the  solid  mass  is  ground,  salted,  and  pressed  into  cakes, 
after  which  it  is  placed  in  a  curing  room  where  it  is  kept 
for  some  time  at  a  temperature  of  13°  C.  There  should  be 
present  also  about  65  to  75  per  cent,  of  moisture  in  the 
curing  room.  If  the  temperature  is  too  high  fat  exudes 
from  the  cheese,  and  too  much  moisture  is  lost.  The  changes 
which  take  place  during  ripening  are  not  purely  bacterial  but 
are  largely  due  to  enzymes.  Some  water  is  lost  by  vapori- 
zation; lactose  is  converted  to  lactic  acid;  and  proteins  are 
hydrolyzed,  many  of  them  to  soluble  products.  Odor  and 
flavor  are  developed  which  impart  quality  to  the  cheese.  The 
result  of  the  various  changes  is  a  decided  improvement  in 
the  palatability  and  digestibility  of  the  material. 

Cheshire  cheese  is  made  in  England  from  fresh  milk.  The 
method  and  care  of  cutting  the  curd  and  removal  of  the 
whey  is  important. 

Stilton  cheese  is  made  between  INIarch  and  September,  from 
the  milk  of  cows  fed  only  on  natural  pasture,  and  the  rennet 
is  obtained  from  lambs'  stomachs  and  not  from  calves. 

Camembert  and  Brie  are  soft  cheeses  made  in  France  by 
somewhat  similar  processes,  except  that  during  the  curing 
mold  develops  on  the  outside  and  the  enzyme  changes  are 
more  pronounced  within.  Proteins  are  broken  down  to  a 
greater  extent. 

Roquefort  is  made  from  sheep's  milk  and  during  ripening 
a  green  mold  grows  throughout  the  mass  of  cheese,  breaking 
down  the  protein  compounds  so  as  to  give  it  the  characteristic 
taste  and  odor. 

Limhurger  was  made  in  Belgium  originally,  but  is  now 
considered  strictly  a  German  cheese.  The  curd  is  formed 
at  a  high  temperature,  and  it  is  ripened  at  a  somewhat 
higher  temperature  than  usual,  and  in  a  very  moist  atmos- 


326  MILK  AND  DAIRY  PRODUCTS 

phere.  Under  these  conditions  bacterial  changes  take  place 
to  such  an  extent  that  putrefactive  fermentation  sets  in, 
giving  it  the  high  odor  for  which  it  is  noted. 

234.  Koumiss. — Koumiss  is  a  drink  made  properly  from 
mares'  milk  by  the  nomadic  tribes  of  Asia  Minor.  Mares' 
milk  is  richer  in  lactose  than  is  cows'  milk  and  on  the  addition 
of  old  or  dried  koumiss  part  of  the  lactose  ferments  to  alcohol 
and  carbon  dioxide,  some  of  it  changing  also  to  lactic  acid. 

Kephir  is  a  somewhat  similar  drink  prepared  from  cows' 
milk  by  the  inhabitants  of  the  Caucasus.  Fermentation  is 
caused  by  the  addition  of  the  so-called  kephir  grains,  the 
origin  of  which  is  not  known,  but  which  contain  certain 
microorganisms  capable  of  causing  the  production  of  lactic 
acid,  alcohol,  and  carbon  dioxide  from  lactose.  Both  of 
these  slightly  alcoholic  drinks  are  easily  digested  by  invalids 
and  have  assumed  some  importance  as  drinks  for  medicinal 
purposes. 

235.  Condensed  and  Desiccated  Milk. — For  the  purpose  of 
keeping  milk,  it  is  condensed  by  evaporation  in  a  partial 
vacuum,  with  or  without  the  addition  of  sugar,  to  a  thick 
consistency  of  one-third  to  one-fourth  its  original  volume. 
This  substance  can  be  sealed  up  in  air-tight  cans  and  kept  for 
a  long  time,  being  mixed  with  water  in  various  proportions 
just  before  use.  Desiccated  milk  can  be  made  by  various 
processes,  one  of  which  is  to  spray  the  milk  against  a  rapidly 
revolving  hot  plate  which  instantly  drives  off  the  water  and 
permits  the  collection  of  the  dry  milk  powder.  This  resumes 
its  original  condition  when  it  is  stirred  up  with  water. 

EXERCISES 

1.  What  is  meant  by  a  pseudo-solution?  Where  else  than  in  this  chapter 
has  this  word  been  used?  What  are  the  properties  of  such  a  solution? 
How  does  it  differ  from  a  true  solution? 

2.  How  does  the  specific  gravity  of  milk  change  if  it  is  watered?  If  it 
is  skimmed?     Why? 

3.  What  is  the  difference  between  caseinogen  and  casein?  What  does 
the  suffix  "ogen"  mean?     When  else  has  it  been  used? 

4.  Can  you  explain  why  2  per  cent,  is  usually  the  maximum  amount  of 
lactic  acid  found  in  sour  milk?  What  other  examples  of  a  similar  phenom- 
enon have  been  studied? 

5.  How  could  you  attempt  to  ascertain  the  percentage  of  fat  in  milk? 


REFERENCES  327 

6.  Compare  milk,  cheese,  butter  and  buttermilk  as  to  their  composition; 
as  to  their  relative  value  as  foods,  pound  for  pound;  as  to  the  organ  which 
digests  the  major  portion  of  the  valuable  constituents  of  each. 

7.  What  substances  found  in  milk  produce  the  following  effects:  Sweeten 
milk;  help  to  make  the  bones  of  an  infant;  change  when  souring  takes  place; 
gives  milk  its  color;  are  without  doubt  made  in  the  milk  glands? 

8.  What  properties  common  to  proteins  are  mentioned  in  this  chapter? 

9.  Is  milk  fat  a  compound? 

10.  Why  is  lactose  called  an  aldose? 

11.  What  fat  is  most  characteristic  of  butter? 

12.  Write  the  graphic  formula  of  butyrin  and  of  the  glyceryl  ester  of 
butyric,  lauric  and  oleic  acids. 

REFERENCES 

Barthel.     Milk  and  Dairy  Products. 

McKay  and  Larsen.     Principles  and  Practice  of  Butter  Making. 

Leach.     Food  Inspection. 

Richmond.     Dairy  Chemistry. 


INDEX 


Absorption  of  food  constituents, 

309 
in  soil,  164 

chemical,  165 

physical,  167 
Achroodextrin,  33 
Acid  humus,  141 
phosphate,  210 

availability,  211 

effect  of,  on  soil,  211 

with  farm  manure,  250 
Acidity  of  soil,  225 

artificial,  226 

natural,  226 
Active  organic  matter,  134,  142 
Adipose  tissue,  291 
Adsorption,  167 
Air,  composition  of,  127 

inspired  and  expired,  296 
properties  of,  126 
Air-slaked  lime  as  fertilizer,  233 
Albite,  162 
Alkali  soils,  183 

reclamation  of,  185 
Alkaloids,  64 

Allyl  cyanide  in  oil  of  mustard,  51 
isothiocyanate  in  oil  of  mustard, 

51 
AUyl-propyl-disulphide,  51 
Alummium   minerals   in    the  soil, 

162 
Alunite,  222 
Amber,  56 
Amendments,  188 
American  cheese,  324 
Amides  in  plants,  61 
Amino-acetic  acid,  61 
Amino-acids  in  plants,  61 
Amino-succinamide,  61 
Ammonia,  formation  of,  in  soil,  144 


Ammonia,    loss     of,    from     farm 
manure,  245 

in  plants,  60 
Ammoniacal  copper  carbonate,  274 
Ammonification,  144 
Ammonium  sulphate,  197 
availability  of,  199 
cause  of  soil  acidity  of,  226 
effect  of,  on  soil,  199 
Amylases,  77 
Amylodextrin,  32 
Amyloid,  38 
Amylopsin,  308 
Analyses  of  crops,  106 

how  expressed,  256 
Anhydrite,  160 
Animal,  composition  of,  287-289 

compounds,  299 

starch,  299 
Anorthite,  161 
Antimony  rubber,  60 
Apatite,  155 
Araban,  38 
Arabinose,  38 
Argenine,  61 
Argon  in  air,  129 
Arid  soils,  178 
Arsenous    oxide,    use    in    making 

Paris  green,  268 
Arteries,  293 
Asafetida,  57 
Ash  in  plants,  104 
Asparagine,  61 
Atropine,  65 
Attar  of  roses,  52 
Available  plant  food,  80 


Bacteria  in  air,  130 
in  farm  manure,  245 


330 


INDEX 


Bacteria  in  intestines,  309 

in  milk,  322 

in  soils,  134 
number  of,  138 
Balsams,  definition  of,  55 
Barley  seed,  discussion  of  compo- 
sition of,  111 
Basalts,  176 
Base  goods,  205 

Basic   copper  acetate,   use  of,   in 
making  Paris  green,  268 
carbonate,  use  of,  in  making 
fungicides,  274 

slag,  212 

availability  of,  214 
composition  of,  212 
effect  of,  on  fertilizer  mixtures, 
190 
on  soil,  214 
Baum^  scale,  282  (footnote) 
Bauxite,  163 
Beeswax,  301 
Benzaldehyde     in     oil     of     bitter 

almonds,  50 
Benzoin,  58 
Biennials,  92 
Bile,  308 
Biotite,  162 
Black  alkali,  183 
Blood,  292 

clotting  of,  295 

exchange  of  gases  in,  296 
Bone  phosphate  of  lime,  261 

tankage,  204 
Bone-black,  207 

dissolved,  207 
Bone-meal,  207 
Bones,  289 

raw,  as  a  fertilizer,  206 
Bordeaux  mixture,  275 

use  of,  with  Paris  green,  268 
Brewer's  grains,  111 
Brewing,  use  of  barley  in.  111 
Brie  cheese,  349 
British  gum,  34 
Brown  sugar,  28 
Buhach,  273 
Bulbs,  purpose  of,  92 
Burnt  lime  as  fertilizer,  232 
Butter,  323 
Buttermilk,  323 
Button  lac,  57 
By-product  coke  ovens,  197 


Caffeine,  65 
Calcite,  160 

Calcium    carbonate    as    fertilizer, 
231 
solution  in  soil  moisture,  161 
compounds  in  the  animal,  302 
cyanamide,  200 
fertilizers  as  plant  food,  224 
function  of,  in  plant,  99 
hydroxide  as  fertilizer,  233 
minerals  in  soil,  160 
nitrate  as  a  fertilizer,  195 

in  the  soil,  145 
oxide.     See  Lime. 

amount    of,    in    burnt    lime, 
235 
in  calcium  carbonate,  232, 

235 
in  slaked  lime,  235 
as  a  fertiUzer,  232 
saccharates,  27 
sulphate  as  a  fertilizer,  239 
Cahche,  193 
Calorie,  316 
Calorimeter,  314 

respiration,  314 
Camembert  cheese,  325 
Canada  balsam,  58 
Canaigre,  70 

Cane  sugar,  24.    See  also  Sucrose. 
Caoutchouc,  59 
Capillaries,  293 
Caramel,  58   . 

Carbohydrate,  amount  of,  synthe- 
sized by  plants,  88 
function  of,  in  plant,  91 
in  milk,  318 
Carbohydrates,  absorption  of,  into 
body,  309 
amount  of,  in  plants,  18 
in  the  animal,  299 
function  of,  311 
definition  of,  18 
manufacture  of,  87 
transfer  of,  in  plants,  87 
Carbon  dioxide  in  air,  128 
exhaled  by  man,  129 
given    off   by    burning    coal, 

129 
how  it  gets  out  of  the  blood, 
296 


INDEX 


331 


Carbon    dioxide   in  the  soil,  136, 
137,  153 
used  by  com,  129 
disulphide  in  oil  of  mustard,  51 

use  of,  with  farm  manure,  250 
function  of,  in  plant,  94 
monoxide    poisoning,    cause   of, 
294 

Carburetor,  280 

Carnauba  wax,  46 

Casein,  320 

Caseinogen,  320 

Castor  oil,  43 

Castor-bean  pomace,  204 

Catalytic  agents,  76 

Catechu,  70 

Caustic  lime  as  a  fertilizer,  232 

Cellophane,  37 

CeUuloid,  37 

Cellulose  acetate,  37 

amount  of,  in  different  parts  of 

plants,  35 
general  description,  35 
nitrates,  37 
solvents  for,  36 

Cement  dust,  223 

Chalk  as  a  source  of  lime,  231 

Cheddar  cheese,  324 

Cheese,  324 

Cheshire  cheese,  325 

Chestnut  wood  and  bark  for  tan- 
ning, 70 

Chicle,  60 

Chile  saltpeter,  193 

Chlorine  compoimds  in  the  animal, 
303 
minerals  in  the  soil,  162 

Chlorophyl,  85 

Chyme,  307 

Cinnamic  aldehyde  in  oil  of  cinna- 
mon, 50 

Citral  in  oil  of  lemon,  50 

Citric  acid,  67 

Citronellol  in  oil  of  roses,  52 

Clay  soils,  180 

Coagulation  of  blood,  295 

Cocaine,  66 

Cod-liver  oil,  300 

Cold  manures,  246 

Collagen,  292 

Collodion,  37 

Colophony,  56 

Colza  oil,  46 


Commercial  fertilizers,  188 

Complete  fertilizers,  188 

Composted  manure,  252 

Condensed  milk,  326 

Connective  tissue,  291 

Copal,  56 

Copper  aceto-metarsenite,  268.  See 

Paris  green. 
Corn,  changes  in  composition  of, 
during  growth,   121 
kernel,  structure  of,  93 
oil,  44 

seed,  discussion  of  composition 
of,  112 
Corpuscles,  red,  293  '^ 

white,  294 
Corrosive  sublimate,  276 
Cotton  purification,  38 
seed,  composition  of,  106 
discussion  of,  1 14 
fertilizing  constituents  of,  109 
meal  as  a  fertilizer,  204 
oil,  44 
stearine,  44 
yields,  108 
Cream,  323 
Crop  chemistry,  110 

yields,  108 
Crops,  analyses  of,  108 
classification  of,  105 
composition  of,  106 
Crude  fat  in  plants,  103 
fiber  in  plants,  103 
petroleum,  281 

use  of,  in  making  miscible  oils, 
273 
protein  in  plants,  104 
turpentine,  58 
Cuprammonium    carbonate    as    a 

fungicide,  274 
Curdling  of  milk,  319 
Cutch,  70 

Cyanamid,  availability  of,  201 
effect  of,  on  soil,  202 
as  a  fertihzer,  201 
Cyhnder  oil,  285 


Deep-stall  system  of  caring  for 

farm  manure,  249 
Denitrification,  145 
Desiccated  milk,  326 


332 


INDEX 


Dextrates,  22 

Dextrin,  34 

Dextrose  in  the  animal,  299 

condensation   to,    by   formalde- 
hyde, 87 

general  description  of,  20 
Dextroxides,  22 
Diastase,  77 

importance  of,  in  brewing.  111 
Dicalcium  phosphate  in  fertilizers, 
211,  222 
in  soiLs,  156 
Diffusion  in  the  soil,  169 
Digallic  acid,  69 
Digestible  carbohydrates,  104 

coefficient,  313 
Digestion,  305 
Direct  fertilizers,  188 
Disaccharides,  19 
Disilicic  acids,  157 
Dissolved  bone-black,  208 
Distribution  of  essential  elements 

in  seed  crops,  100 
Divi-divi,  71 
Dolomite,  160 

as  a  fertilizer,  239 

as  a  source  of  lime,  231 
Double  potash  manure  salt,  221 
Dragon's  blood,  57 
Drainage-water,     composition    of, 

172 
Dried  blood,  availability  of,  203 
black,  202 
as  a  fertilizer,  202 
red,  202 

fish,  204 

meat  as  a  fertilizer,  203 
Driers  for  linseed  oil,  44 
Drying  oils,  constituents  of,  43 

definition  of,  41 
Dust  in  air,  130 


E 


Ebonite,  60 
Elastin,  292 

Elements,    essential,   for   animals, 
287 
distribution  of,  in  seed  crops, 

100 
for  plant  growth,  80 
function  of,  in  plants,  94 


Elements,  form  in  which  absorbed 
by  plants,  82 
how  absorbed  by  plants,  83 
Emulsifier,  273 
Emulsion,  definition  of,  271 
Encrusting  substances,  35,  38 
Enzymes,  76 
Epithelial  tissue,  291 
Erythrocytes,  293 
Erythrodextrin,  33 
Essential  oils,  47.  See  also  Volatile 

oils. 
Ethereal  oils,  47.    See  also  Volatile 

oils. 
Eu^enol  in  oil  of  bitter  almonds,  49 

of  cloves,  50 
Excrement,  composition  of,  242 
liquid,  of  farm  animals,  242 
mixed,  amount  of  plant  food  re- 
covered in,  244 
influence  of  animal  on  compo- 
sition, 244 
of  food  on  composition,  244 
solid,  of  farm  animals,  241 


F 


Farm  manure,  action  of  molds  in, 
247 
bacteria  in,  245 
composition  of,  244 
compounds  in,  244-245 
decomposition  of,  aerobic,  245 

anaerobic,  245,  247 
definition  of,  241 
fresh,  how  to  use,  251 
losses  of,  247 

prevention  of,  248 
chemical,  249 
mechanical,  248 
an  unbalanced  fertilizer,  253 
value  of,  253 

well  decomposed,  how  to  use, 
251 
Fat  in  milk,  319 
Fats,  absorption  into  body,  310 
animal,  300 

composition  of,  291 
digestion  of,  in  intestines,  308 
function  of,  in  the  animal,  311 
Fatty  acids,  classification  of,  42 
in  milk,  320 


INDEX 


333 


Fatty  acids,  saturated,  42 
unsaturated,  42 

tissue,  291 
Feces,  241 

Feed,  distinction  from  food,  304 
Feeding  standards,  316 
Fehling's  solution,  21 
Feldspar,  lime,  161 

potash,  158 

soda,  162 
Fertilizer,  analysis  of,  260 

mixtures  to  be  avoided,  190 
Fertilizers,  choice  of,  191 

commercial,  188 

.complete,  188 

definition  of,  187 

direct,  188 

incomplete,  189 

indirect,  188 
Fertilizing  constituents   of   crops, 

109 
Fibrin,  295 
Fibrinogen,  293,  295 
Film,  water  in  the  soil,  170 
Fire  point,  282  (footnote) 
Fish  scrap,  204 

Fixed  oils,  general  definition  of,  40 
methods  of  extraction  of,  41 
properties  of,  40 
Flash  point,  282  (footnote) 
Flax  seed,  composition  of,  106 
discussion  of,  114 
fertilizing  constituents  of,  109 
yields  of,  108 
Floats,  208 
Fluorides,  use  with  farm  manure, 

250 
Food  constituents,  305 

function  of,  in  the  animal,  311 

definition  of,  304 

effect  of,  on  quality  of  milk,  321 

for  seedling,  76 

for  soil  bacteria,  138 

value,  expressions  for,  313 
Form  in  which  plant  food  elements 

are  absorbed,  82 
Formaldehyde  candles,  277 

formation  of,  in  leaf,  87 

as  a  fungicide,  276 
Formalin,  276 

Four-cycle  type  of  gas  engine,  279 
Frankincense,  58 
Fructose,  23.   See  also  Levulose. 


Fruit  crops,  composition  of,  106 
discussion  of,  114 
fertilizing  constituents  of,  109 
yields  of,  108 
sugar,  23.    See  also  Levulose. 
Fungi,  how  destroyed,  265 
Fungicides,  274 


Gallic  acid,  69 

GaUs,  71 

Gam  bier,  71 

Gamboge,  58 

Gas  engine,  279 

Gaseous   exchange    in    the  blood, 

296 
Gases   in    blood,   composition  of, 
297 

in  soil,  153 
Gas-lime  as  a  fertilizer,  239 
Gasoline,  283 
Gastric  digestion,  306 

juice,  306 
Geraniol  in  oil  of  roses,  52 
German  potash  deposits,  216 
Germination,  conditions  for,  52 

of  seed,  52 
Gliadin,  112 
Gluco-glucoside,  30 
Glucolin,  30 
Glucose,  20.    See  also  Dextrose. 

commercial,  22 
Glucosides,  definition  of,  21 
Glutamine,  62 
Glycerine,  42 
Glycocoll,  61 
Glycogen,  299 
Grains,  composition  of,  106 

fertilizing  constituents  of,  109 

yields  of,  108 
Granite,  175 

Grape  sugar,   20.     See  also  Dex- 
trose. 
Gum  arabic,  39 
Gum-resins,  definition  of,  56 
Gums,  39 
Guncotton,  37 
Gutta  percha,  60 
Gypsum  as  a  fertilizer,  239 

in  the  soil,  160 

use  of,  with  farm  manure,  249 


334 


INDEX 


HiEMOGLOBIN,  293 

Hair  as  a  fertilizer,  205 
Halite,  162 
Hard  rubber,  60 

water,  172 
Hay,  116 

chemical  change  in  making  of, 
117 

crops,  changes  in  composition  of 
during  making,  118 
Heat  caused  by  germination,  75 

production  in  the  animal  body, 
314 
Height  of  air,  125 
Hellebore,  264 

Hemlock  wood  and  bark  for  tan- 
ning, 70 
Home  mixing  of  fertilizers,  189 
Hoof  as  a  fertilizer,  205 
Horn  as  a  fertilizer,  205 
Hornblende,  161 
Hot  manures,  246 
Humid  soils,  178 
Humus,  139 

composition  of,  141 

properties  of,  140 
Hydrated  lime  as  a  fertilizer,  233 
Hydrocarbons  in  crude  petroleum, 

281 
Hydrocyanic  acid  gas,  269 
in  linseed  press  cake,  45 
in  oil  of  bitter  almonds,  49 
Hydrogen  in  air,  129 

function  of,  in  plant,  94 


Iceland  spar,  19 

Igneous  rocks,  174 

Inactive  organic  matter,  134,  143 

Incomplete  fertilizers,  189 

Indirect  fertilizers,  188 

Inoculation  of  soils,  150 

Inorganic  acids  in  soil,  155 

elements,  function  of,  in  animal, 
313 

material,  use  of,  by  plant,  85 
Insecticides,  external,  269 

internal,  267 
Insects,  how  destroyed,  264 


Intermolecular  respiration,  89 
Intestinal  digestion,  307 

juice,  307 
Inuhn,  39 
Invert  sugar,  27 
Invertase,  308 
Iodine  compounds  in  the  animal, 

303 
Iron  compounds  in  the  animal,  302 

function  of,  in  plant,  100 

minerals  in  soil,  161 


K 

Kainite,  221 
Kaolin,  159 
Kaolinite,  159 
Kaolinization,  159 
Kelp,  221 
Kephh",  326 
Keratin,  291 
Kerosene  emulsion,  270 

how  made,  282 
Kino,  70 
Koumyss,  326 


Lac,  57 

Lactalbumin,  320 

Lactase,  308 

Lacteals,  310 

Lactic  acid  production  in  milk,  319 

Lactose,  318 

Land  plaster,  238.    See  Gypsum  as 

a  fertilizer. 
Lard,  300 
Latex,  59 
Lavas,  176 

Lead  acetate,  use  of,  in  making  lead 
arsenate,  267 
arsenate,  267 

use  of,  with  Bordeaux  mixture, 
276 
with  lime-sulphur,  273 
nitrate,  use  of,  in  making  lead 
arsenate,  267 
Leaf,  structure  of,  86 
Leather  as  a  fertilizer,  205 
Lecithin,  description  of,  46,  47 
Legumes,  composition  of,  106 


INDEX 


335 


Legumes,  discussion  of  composition 
of,  114 
fertilizing  constituents  of,  109 
yields  of,  108 
Leucite,  160 
Leucocytes,  294 
Levulates,  23 
Levulin,  27 
Levulo-glucoside,  27 
Levulose,   general  description   of, 

23 
Lignification,  36 
Lignin,  38 
Limburger,  325 

Lime,    amount    of,    removed    by 
crops,  225 
in  fertilizers,  225 
availability  of,  233 
in  basic  slag,  214 
checking  plant  diseases,  238 
definition  of  term,  231 
effect  of,  on  fertilizer  mixtures, 
190 
harmful,  238 
on  soil,  235, 
from  acetylene  plant  as  a  fer- 

tiizer,  239 
improving  soil  texture,  238 
making    phosphorus    available, 
238 
potassium  available,  238 
neutralizing  acids,  235 
nitrogen,  200 
as  a  plant  food,  224 
requirement,    how    determined, 

259 
use  of,  with  farm  manure,  251 
Limestone,  176 
as  a  fertihzer,  231 
soils  become  acid,  229 
Lime-sulphur,  boiled,  271 

self-boiled,  277 
Limonene  in  oil  of  lemon,  50 
Limonite,  161 
Linoleic  acid,  45 
Linolenic  acid,  43 
Linseed  oil,  44 
Lipases,  77 
Litter,  243 
amount   of   ammonia   absorbed 
by,  243 
of  water  absorbed  by,  243 
composition  of,  243 


Loam  soils,  180 
Lubricants,  284 
Lump  lime  as  a  fertilizer,  232 
Lymph,  298 

glands,  298 

vessels,  298 


M 

Maonesian  lime,  use  of,  239 
Magnesium,  function  of,  in  plant, 
100 

minerals  in  the  soil,  162 
Malic  acid,  68 
Malt  sprouts.  111 

sugar,  29.     See  also  Maltose. 
Maltase,  308 

Maltobiose,  29.    See  also  Maltose. 
Maltodextrin,  33 

Maltose,  general  description  of,  29 
Mangrove,  70 

Manure.    See  Farm  manure,  241, 
et  seq. 

in  formation  of  humus,  143 
Marl  as  a  source  of  lime,  231 
Marrow,  289 
Mashing,  111 
Mass  action,  166 
Mastic,  57 
Meat  meal  as  a  fertilizer,  203 

tankage,  203 
Menhaden  oil,  300 

use  of,  in  making  miscible  oils, 
273 
Menthol  in  oil  of  peppermint,  51 
Mercerized  cotton,  36 
Mercuric  chloride  as  a  fungicide, 

276 
Metamorphic  rocks,  174 
Metasilicic  acid,  157 
Methyl  salicylate  in  oil  of  winter- 
green,  55 
Milk,   adulteration  and  preserva- 
tion of,  322 

composition  of,  318 

digestion  of,  in  stomach,  307 

fat,  319 

inorganic  salts  in,  321 

physical  appearance  of,  318 

secretion,  321 
Minerals  in  soil,  155 

factors  of  solubility  of,  163 


336 


INDEX 


Miscible  oils,  273 
Moisture  for  soil  bacteria,  138 
Molds  in  farm  manure,  247 
Monocalcium  phosphate  in  fertil- 
izers, 210,  212 

in  soils,  156 
Monosaccharides,  19 
Morphine,  66 
Movements  of  dissolved  substances 

in  soil,  168 
Muriate  of  potash,  a  cause  of  soil 
acidity,  228 

as  a  fertilizer,  218 
Muscovite,  160 
Muscular  tissue,  289 
Myosin,  291 
Myosinogen,  291 
Myrobalans,  71 
Myrosin  in  oil  of  mustard,  51 
Myrrh,  58 


N 


Naphtha,  282 
Neatsfoot  oil,  300 
Neutral  humus,  142 
Nicol  prism,  19 
Nicotine,  66 

sulphate,  as  an  insecticide,  274 
Nitrate  of  soda,  as  a  fertilizer,  193 

in  tobacco  waste,  223 
Nitrates,  formation  of,  in  soil,  144 

in  plants,  60 
Nitrification,  144 
Nitrites,  formation  of,  in  the  soil, 

144 
Nitrogen  in  air,  128 
amount  added  to  soil  by  clover 
and  alfalfa,  147,  150 
in  coal,  197 
changes  in  farm  manure,  245,  el 

seq. 
compounds  in  the  air,  130 
equal  to  ammonia,  262 
fixation,  146 
non-symbiotic,  147 
symbiotic,  147 
function  of,  in  plant,  98 
importance  of,  in  fertiUzers,  192 
loss  of,  in  farm  manure,  247 

prevention  of,  248,  249 
in  soil,  153 
Nitrogen-free  extract,  104 


Nitrogenous  extractives,  291 

fertilizers,  192 
Nutgalls,  71 


Oak  bark  for  tanning,  70 
Oat  seed,   discussion  of  composi- 
tion of,  112 
Oil,  76 

of  amber,  66 

of  bitter  almonds,  49 

of  cinnamon,  50 

of  cloves,  50 

function  of,  in  plant,  .91 

of  lemon,  50 

manufacture  of,  by  plant,  89 

of  mustard,  51 

of  onion,  51 

of  peppermint,  51 

of  roses,  52 

of  sassafras,  52 

of  thyme,  52 

transfer  of,  in  plant,  91 

of  turpentine,  53 

of  wintergreen,  55 
Oleic  acid,  43 
Olein,  definition  of,  43 
Oleo  oil,  324 
Oleomargarine,  325 
Oleoresin,  definition  of,  55 
Olibanum,  58 
Olive  oil,  45 
Optical  activity,  19 
Organic  acids  in  animal,  301 
in  plants,  67 
in  soil,  137,  155 

matter  in  arid  soils,  178 

decomposition  of,  in  soils,  136 
factors  affecting  rate  of, 
137 
in  sand  soils,  179 
in  soils,  133 

functions  of,  142 
loss  of,  143 
Orthoclase,  158 
Ossein,  289 
Otto  of  roses,  52 
Oxalic  acid,  68 
Oxidases,  78 
Oxygen  in  air,  128 

consumed  by  burning  coal,  128 


INDEX 


337 


Oxygen,  function  of,  in  plant,  95 

for  germination,  74 

how  it  gets  into  blood,  296 

in  soil,  153,  155 

used  by  man,  128 
Oxyhaemoglobin,  293 
Oyster  shells  as  source  of  lime,  231 


Palmitic  acid,  42 
Palmitin,  definition  of,  43 
Pancreatic  juice,  308 
Paper,  38 
Paraform,  277 
Paris  green,  268 

use  of,  with  Bordeaux  mixture, 
276 
with  lime-sulphur,  273 
Pasteurization  of  milk,  322 
Peanut  oil,  45 
Peat  soils,  181 
Pectins,  39 

Pentacalcium  silico-phosphate,  212 
Pentosans,  38 
Pepsin,  307 

Persian  insect  powder,  273 
Phosphate  fertilizers,  206 
Phosphoric  acid,  citrate  soluble,  in 
fertilizers,  261 
importance  of,   in  fertilizers, 

206 
reverted,  in  fertilizers,  261 
total,  in  fertilizers,  261 
water    soluble,    in    fertilizers, 
261 
Phosphorus,   changes  of,   in  farm 
manure,  246 
compounds  in  animal,  301 
function  of,  in  plant,  95 
loss  of,  in  farm  manure,  247 

prevention  of,  248 
mmerals,  155 
in  soil,  solution  of,  156 
Pinene  in  oil  of  turpentine,  53 
Plant,  composition  of,  81 
food,  available,  80 
definition  of,  80 
how  absorbed  by  plant,  83 
in  soil,  186 
unavailable,  80 
Plasma,  293 
Plaster  of  Paris,  160 


Polariscope,  20 

Polarized  li^ht,  19 

Polysaccharides,  30 

Potash  equivalent  to  sulphate,  262 
fertilizers,  216 

importance  of,  in  fertilizers,  216 
manure  salt,  218 
salts,  effect  of,  on  fertilizer  mix- 
tures, 190 
use  of,  with  farm  manure,  250 

Potassium  carbonate  in  soils,  159 
in  wood  ashes,  221 
changes  in  farm  manure,  246 
chloride  as  a  fertiUzer,  218 
compounds  in  animal,  302 
cyanide,  use  of,  in  making  hydro- 
cyanic acid  gas,  270 
function  of,  in  plant,  96 
loss  of,  in  farm  manure,  247 

prevention  of,  248 
minerals  in  the  soil,  157 

solution  of,  159 
myronate  in  oil  of  mustard,  51 
sulphate  as  a  fertilizer,  220 

Preservatives,  use  with  farm  man- 
ure, 250 

Press  cake,  41 

Pressure  of  air,  125 

Products  of  oxidation  in  seeds,  75 

Proteases,  78 

Protein,  function  of,  in  plant,  91 
manufacture  of,  by  plant,  90 
transfer  of,  in  plants,  91 

Proteins,  absorption  of,  into  body, 
247 
composition  of,  62 
digestion  of,  in  intestines,  308 

in  stomach,  307 
functions  of,  in  animal,  311 
in  milk,  320 
properties  of,  62 

Protoplasm,  91 
composition  of,  91 

Ptyalin,  305 

Pyrethrum,  273 

Pyroxylin,  37 


Quartz,  162 
Quebracho,  70 
QuickUme  as  fertilizer,  232 
Quinine,  66 


338 


INDEX 


Rapeseed  oil,  46 

Raw  bones  as  a  fertilizer,  206 

Red  corpuscles,  293 

rubber,  60 
Rennin,  307 
Rescues,  55 
Resin  ducts,  55 
Resins,  properties  of,  55 
Respiration  calorimeter,  314 

in  plants,  88 
l)r<)ducts  of,  89 

in  seeds,  74 

due  to  oxidases,  78 
Respiratory  quotient,  298 
Reversion  of  acid  phosphate,  211 
Ripening  of  cheese,  325 
Rise  of  alkali,  184 
River  water,  composition  of,  172 
Rock  lime  as  fertilizer,  232 

phosphate,  208 

use  of,  with  farm  manure,  248 
Rocks,  soil  forming,  174 
Root  hairs,  83 
Roots,  function  of,  85  ' 

purpose  of  fleshy,  92 

selective  action  by,  83 
Roquefort  cheese,  325 
Rosin,  56 

oil,  56 
use  of,  in  making  miscible  oils, 
273 

spirit,  56 
Rubber,  59 
Ruminants,    gastric   digestion   of, 

306 
Rye  seed,  discussion  of  composition 

of,  112 


Saccharates,  27 

Saccharimeter,  20 

Saccharose,  24.    See  also  Sucrose. 

Safrol  in  oil  of  sassafras,  52 

Saliva,  305 

Salivary  digestion,  305 

Salting  out  proteins,  64 

Sand  soils,  179 

Sandarac,  57 

Sandstones,  177 

Sarcolactic  acid,  291 

Sawdust,  use  as  litter,  243 


Schweitzer's  reagent,  36 

formula  for,  269 
Scrape,  58 

Sedimentary  rocks,  174 
Seedling,  food  for,  76 
Seeds,  production  of,  92 
Selective  action  by  roots,  83 
Separator  for  cream,  323 
Serum,  295 

albumin,  293 
Shales,  177 

Shavings,  use  as  litter,  243 
Shellac,  57 
Siderite,  162 
Sieve  tubes,  88 
Silage,  121 

making,    chemical   changes     in, 
121 
Silicic  acids,  157 
Silicon  compounds  in  animal,  303 

minerals  in  soil,  162 
Silk,  artificial,  37 
Slaked  lime  as  fertilizer,  233 
Sludge  acid,  use  in  making  fertil- 
izers, 282 
Soap,  41 
Soda  cellulose,  36 

process  for  making  paper  pulp, 
38 
Sodium  arsenate,  use  of,  in  making 
lead  arsenate,  267 

compounds  in  animal,  302 

cyanide,  use  of,  in  making  hydro- 
cyanic acid  gas,  270 

minerals  in  soil,  162 

nitrate,  availabiUty  of,  194 
effect  of,  on  soil,  194 
as  a  fertilizer,  193 
Soil  acidity,  225 

how    determined,    259.      See 
Lime  requirement. 

analysis,  256 

and  subsoil,  182 

composition  of,  132 

distinction  of,  from  subsoil,  182 

functions  of,  132 

solvents,  154 
Soils,  composition  of,  181 

kinds  of,  177 

weight  of,  181 
Solubility  of  soil  minerals,  factors, 

163 
Soluble  cotton,  36 


INDEX 


339 


Soluble  oils,  273 

Specific  rotation,  20 

Spectrum,  85 

Sperm  oil,  301 

Starch,  76 
animal,  299 
amount  of,  in  crops,  31 
commercial,  how  made,  34-35 
digestion  of,  in  intestines,  308 

in  mouth,  305 
formation  of,  from  dextrose,  87 
general  description  of,  31 
grains  acted  on  by  diastase,  78 
iodide,  31 
paste,  31 

Stassfurt  potash  deposits,  216 

Steamed  bone,  207 

Steapsin,  308 

Stearic  acid,  42 

Stearin,  43 

Stem  and  leaf  crops,  composition 
of,  107 
discussion  of,  114 
fertilizing    constituents    of, 

110 
yields  of,  108 

Sterilization  of  milk,  322 

Stick  lac,  57 

Stilton  cheese,  325 

Stone  lime  as  fertilizer,  232 

Strychnine,  66 

SubsoU,  182 

Succinic  acid,  56 

Sucrose,  general  description  of,  24 
pure,  how  made,  27-28 

Sucroxides,  27 

Sugar  beet,  sugar  content  of,  25 
cane,  sugar  content  of,  25 
how    made    from    sugar    beets, 
28-29 
cane,  28-29 

Sugars,  18 

Sulphate  of  potash,  cause  of  soil 
acidity,  228 
as  a  fertilizer,  220 

Sulphite  process  for  making  paper 
pulp,  38 

Sulphur  dioxide  in  air,  131 
function  in  plant,  99 
minerals  in  the  soil,  160 

Sulphuric  acid,  use  with  farm  man- 
ure, 250 

Sumach  leaves  for  tanning,  69 


Sunflower  oil,  46 

Sun's  rays,  use  of,  in  synthesizing 

plant  substances,  85 
Superphosphate,  210.  See  also  Acid 

rhosphate. 


Tallow,  300 
Tankage,  203 
Tannic  acid,  68 
Tannins,  69 
Tartaric  acid,  68 
Temperature  of  air,  126 

for  soil  bacteria,  138 
Tetracalcium  phosphate  in  basic 

slag,  212 
Theine,  65 
Theobromine,  67 
Therm,  316 
Thomas  slag,  212 
Thymol  in  oil  of  thyme,  52 
Timothy,  changes  in  composition 

during  growth,  120 
Tobacco  as  an  insecticide,  274 

waste,  223 
Tolu,  59 
Tracheae,  83 

Tricalcium   phosphate,    in   bones, 
289 
in  fertilizers,  206,  208,  212 
in  soils,  156 
Trisilicic  acids,  157 
Trypsin,  308 
Tubers,  purpose  of,  92 
Two-cycle  type  of  gas  engine,  280 
Tyrosine,  62 


Unavailable  plant  food,  80 
Urea  in  farm  manure,  decomposi- 
tion of,  245 
Urine,  242 


Valonia,  71 

Vegetable   crops,   composition   of, 
107 
discussion  of,  115 


340 


INDEX 


Vegetable    crops,    fertilizing    con- 
stituents of,  110 

yields  of,  109 
Veins,  292 
Vim,  309 
Virgin  dip,  58 

soils  become  acid,  230 
Viscoid,  37 
Viscose,  37 
Vivianite,  162 
Volatile  oils,  classification  of,  49 

definition  of,  47 

methods  of  extraction  of,  48 

properties  of,  48 


W 

Waste  water  in  soil,  172 

Water,  absorption  of,  by  seed,  74 
amount  of,  in  seeds,  73 
determination  of,  in  plants,  103 
function  of,  in  plant,  95 
for  germination,  73 
passage  of,  into  plant,  83 
in  soil,  composition  of,  170 
soluble  arsenic,  267  (footnote) 
vapor  in  air,  126 
withdrawal  of,  from  roots,    84 

Wavellite,  163 


!  Waxes,  46 

Weende     method     for     analyzing 
foods,  102 

Weight  of  air,  125 

Well-rotted  manure,  247 

Wheat  seed,  discussion  of  compo- 
sition of,  112 

Whey,  325 

White  alkali,  183 
corpuscles,  294 

Wood  ashes,  221 
gum,  39 

Wool  waste  as  a  fertilizer,  205 


Xanthoproteic  reaction,  63 
Xylan,  39 
Xylose,  39 


Yellow  dip,  58 
Yields  of  crops,  108 


Zein,  63 


UNIVERSITY  OF  CALIFORNIA,  LOS  ANGELES 
THE  UNIVERSITY  LIBRARY 


MAY  2 


Th 


DEC  2  8  1953 

REC'D  LD-URC 


k  is  DUE  on  the  last  date  stamped  below 


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Form  L-» 
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THE  LIBRARY 


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